Hi Johnny Boy, I know a house where this has been done and I'll give you my two cents on observation alone. Clearly you need to factor in the current health and mobility and plan for the future and any changes in mobility. It's sounds harsh but you have to accept this and plan for it.
The room I saw had an open plan shower, with the floor slightly curved to drain the water. That way there was no basin/shelf for the shower i.e. nothing to step/trip over. It also means that if a wheelchair is involved, space permitted, there are few barriers. Clearly the doors and layout of the rest of the house needs to take that into account.
I also noticed that the heaters was activated by a pull down cord so this could be adjusted to suit the position of the purpose. Also, none of the sinks, controls were set too high either.
I did a quick google search and found two points :
[broken link removed]
'If elderly share your bathroom its worth installing a fold down seat in the shower or fitting the bath with rails to make getting in and out easier. '
and
http://www.dulley.com/docs/f556.htm
'Also, the elderly often have reduced temperature sensitivity and can unknowingly scald themselves'
The latter may be more sales oriented.
Also, there may be grants available to cover the cost - ring your county council.
I've got no experience in this area bar my observations but I'm sure you will get a lot of help here. It's possible some organisations dealing with elderly can advise.
Good luck with it all.