ITA that the flannelette backing would be good to help them stay in place.
Likewise ties could be a good idea ... or put velcro on for a quick attachment and release.
If you're making them as generic gifts to a facility, you'd be best to ask them if there are any specifics re size, types of fabrics, etc. As items owned and used by the home, they may have requirements to be met knowing what has worked in the past for their residents and staff. Better to ask up front, than to be disappointed when your kindness is turned away.
As suggested, if making for a specific individual(s), let them guide you in their wish list!!
Congratulations for your thoughtfulness.