What product do you recommend to protect a mattress from incontinence that offers good protection, but is still comfortable?

Gone are the days when waterproof meant crinkly plastic, when I bought my last mattress I was told I could return it as long as I bought the waterproof cover they also sold - it has a soft fabric top and is still 100% waterproof many years later (as with all of these items just don't use any bleach as that can destroy the lining).
You will also want to use a washable quilted bed pad, I suggest getting the larger ones as they are not only more effective but will also be less noticeable.
https://www.agingcare.com/products/quilted-bed-pad-204739.htm

Check Amazon. I found some excellent mattress protectors made from bamboo. They stand up to repeated washing and are as comfortable as the mattress alone. The washable pads between the sheet and the mattress cover are great as well.

Walmart carries a waterproof protector. Remove the sheet and just wipe the protector. I found out about them when I moved mom to MC and was a required item. Next to protect sheets you can get washable or disposable pads. Of course, you will put them over the bottom sheet so he will see. Just encourage to him that they will make your care easier. Otherwise he goes into care

With my wife, I started with the usual protective mattress pad underneath the sheet, with a large towel on top of it, which made it somewhat more easily changed, but was less noticeable. But the fitted sheet would still have to be laundered at times. I then changed to placing the mattress pad and covering towel directly on the fitted sheet; if changing was needed then, it only involved the towel and pad. Discussion with our partners is also important, and necessary; they need to understand the health reasons for doing what we do, and need to come to acknowledge the impacts on their own health, and the demands that their care places on us caregivers. These can be delicate issues to discuss, but when approached matter-of-factly, compassionately, and not "accusingly," it will benefit all.

I got my Mom washable incontinence bed pads. Because my Mom liked to get off the bottom as well as the side of the bed and because she moved all night, the bed pad had to go from "top" to edge of bed (size was 80 x 36) I got them from Amazon.

There was no plastic noise to them. We put them between the mattress pad and the fitted sheet.

Worked great...and when folded, also worked for protection while she was in the wheel chair.

P.S. I would start now so that he will get used to the "little extra cushion" under him.

I found a great one on Amazon for around forty dollars, very soft and comfortable, not plastic, and works wonderfully and washes great. Get two, you will want a backup. And do not be tempted to get a cheaper one, you will regret that wasted purchase. I learned the hard way.

I bought my dad a no noise waterproof mattress protector -so it’s not made of loud paper so you can’t hear it when you move- technology getting quite clever on that -found on amazon. I then purchased a mattress protector sheet/pad
dl that’s a waterproof strip of material which has flaps to tuck in and goes across middle of bed- washable
got a couple so when ones in the wash I have another
so I have two lots of protection plus his incontinence underwear. At night he wears the disposable incontinence highest strength briefs under his incontinence boxer shorts
and that works for him
i got a nappy bin but I don’t call it that and he’s quite pleased with it and in a routine now to put them into the no of our bin himself
in fact he goes one further by putting them into those nappy bin bags then into his nappy bin - no odours and all clean
oh
i did also invest in duvet cover protector sheets so waterproof and wipeable - you put a duvet cover over them
in the beginning I had him lay on a thin summer duvet - in the mattress protector -
in a duvet cover
sounds a lot and prob is !
but I’m left with a clean house and now it’s routine
and I just find I’m washing far less
wipe down jobs with a cloth and spray disinfectant
hardly any work at all now
to the wet bet nonsense I was dealing with and smells!
good luck

My father was incontinent when I became his caregiver. I kept him in pull on diapers because he didn't always know when he had to go. Plus the diapers were convenient for when we had to leave the house.
At night I used a vinyl mattress cover to protect the mattress and used a large mattress pad between him and the fitted sheet. This worked well in protecting the mattress, but I had to wash his sheets every day because he had accidents or removed the diaper during the night.
Dad had dementia, so you may not have success doing what I was able to do. Also, you may already know this, but someone I had consulted about Dad's care told me that adding a cup of white vinegar to the wash water would prevent the urine smell in the sheets. I wish you success.

I found a large pad that is washable but still protects mattress. It is not noticeable under sheet and makes no noise.

I purchased a pack of two waterproof mattress pads from Amazon. They are called Cool Shields and are excellent. I also bought a padded mattress cover that I placed over the original waterproof cover that is part of the mattress. II did this to make the hospital bed mattress more comfortable. I placed a large disposable waterproof underpad on top of the mattress cover, then the sheet and then the Cool Shield waterproof pad from Amazon, The Cool Shield pad was quite large and fit from side to side of the bed. The sheet stayed dry and the mattress pad stayed dry.

Here's another tip. To keep the padded mattress cover from slipping around on the plastic mattress, I bought a roll of rubberized slip proof liner (that is used to keep small floor mats from slipping) and placed it under the mattress cover. It kept everything from slipping and sliding around.