Need nice warm night gowns that open in the back. Any ideas?

Do a google search for Adaptive nightgowns to find a few sources for open-in-back nightwear. Check not only their prices but the shipping costs, too. I found a few that have a flat $9 shipping charge, so buying more than one (if you are eventually going to want more than one) is a way to economize.

If Mom has some front-opening gowns she likes and if you are handy with a sewing machine (or have a friend who is) you could make a long slit in the back, bind one edge and sew a wide flap to the other edge. The flap would fasten to the other side with some Velcro or snaps -- just nothing that would be uncomfortable to sleep on. (If you lived close to me I'd get a nice gown from the thrift store and experiment for you!)

Silverts has a sale on, $33.46, unfortunately $10 shipping unless you buy more than $150.
I know the prices seem extreme but there is no way around it, trying to adapt normal nightgowns so they overlap like the adaptive ones just isn't practical. I was lucky to find some for mom from a local supplier that is going out of business

Oooo, I've just checked Buck and Buck and they have good prices - only $20, have you looked there?