I have just read through this thread and have nothing but admiration & the deepest respect for all of you that are working so hard at keeping your loved one at home as long as possible.
I had to admit defeat with my Mom last year and put her in a home and I am a fairly fit bloke in his 50's and Mom never weighed more than 8 stone so I doff my virtual cap to you all.
Mom, although only just about accepting that she needed help, insisted on always being able to go upstairs to bed. At first she was able to use the stair lift (on a short, straight run Cost £1300 in 2011) but latterly transfers were getting difficult and I also had to operate it for her via remote control.
In the bedroom Mom had a very small ensuite (less than 6' x 3')with a step in shower & a sink. This I had converted into a wet room (cost £2500) and also managed to squeeze in a toilet with enough room for a commode wheel chair to get in.
One of the fitters who came out was in a similar situation with his Dad looking after his Mom however she
needed to be hoisted. I highlight this point as it is something you all may have to consider in the future.
Being upstairs 2 hoists will be needed as you will need one downstairs as well, and in the case of the fitter his Mom's bedroom was too small to accommodate one.
The only solution was for his Mom to accept living downstairs and he converted the downstairs toilet into a wet room. It was small at only 4'x3' but kept the toilet and fitted a shower over it. He said that his Dad's workload dropped significantly with the problem of getting up & down the stairs now gone and his own sleep improved giving him more energy. Although it had not happened it would also have been better if his Dad ever had to go into hospital and a live in carer/relative was need during that time.
We discussed how this could be achieved in Mom's house when the time came. The access to the downstairs loo was difficult for a wheelchair but he said that it would not be difficult to fit a similar size wet room (4'x3') with toilet either in the lounge (a chair would have to go) or in the kitchen (the dining table would have to smaller).
Sorry for the ramble but with the cost of that lift, how much use it might be in the future and the space needed for a wet room not much more I just thought I would offer an alternative.