You are smart to be thinking about this now!
We built a separate guest cottage for our parent's use (or, for a caregiver, should we need one, someday). It is 100% wheelchair/walker-accessible
Make sure your doorways are wide enough for a full-size wheelchair and that bathrooms are big enough for a wheelchair to turn around easily. Sinks that are wall-mounted make it easier for a wheelchair to access. Illuminated switchplates make it easier to turn on the lights in the dark (and guide a person to the door area). Door handles, rather than knobs. Hardwood floors (or, a tightweave carpet, like berber) make walking safer (or, for a walker/wheelchair to roll over).
There needs to be enough space in the bedroom for a wheelchair to turn around as well as fit easily next to the bed.
Blinds/curtains with pulls that can be reached and easily used from wheelchair height.
The bathtubs with doors are
wonderful (pricey), especially if you know baths are the preferred method of bathing. I visit my Mom three times a week at her assisted living residence to assist her with the step-in tub, and bathing her is very easy with that tub (assures her cleanliness, too, and keeps me dry, versus trying to help her shower!). (((I'm not sure, but you might be able to get one through insurance if a doctor writes and RX for the person in need. I can find out, if you want!)))
But, given their price, a walk-in/roll-in shower is great, too (we have this in our guest cottage). Get an adjustable, hand-held shower head (it can move up and down on a vertical bar and lock at any height). That is what we have in our guest cottage. It also has a built-in seat. It is big enough for a walker or wheelchair to fit, as well.
There is a company that makes a bottom-of-the-tub/shower brush-on product that is no-slip (hotels use it in their tubs). Invisible, easy to clean and works. I can find the name, again, if you want. No more in-tub/shower suction-cupped mats. By the way, those types of rubber mats with the suction cups on the bottoms will NOT adhere to textured tub bottoms. I'll take a smooth bottomed tub anytime over the textured!
The guest cottage counters are at bathroom height, rather than kitchen height, in both the bathroom and the kitchen areas. The upper cabinets all have knobs (easier to reach with a "grabber" than those without any hardware).
Faucet handles that are easy to use (NOT those single "crystal-look" knobs). A higher, goose-neck faucet is nice, too.
Grab bars, built into the studs
, near the bed, toilet, shower and doors (elderly tend to grab the door for support and doors do not hold still!).
In the bathroom, make sure there is room for a grab bar on either side of the toilet to assist in rising. This can be built-in or freestanding. They are lifesavers and help with independence. Nobody likes having help getting up from a toilet!
Make the toilets "comfort-height", easier to use for everyone (except short, little children
I like a stainless sink, as some meds can stain other materials.
Bi-fold or accordion-type closet doors are nice and easier to use than sliding doors, if you are in a wheelchair or use a walker. Less moving needed.
A very low bedframe allows easier access to their bed (it is very difficult for the elderly to climb UP into a bed!).
Hooks in the closet and on the backs of doors at waist-height make it easier to hang and quickly access often-used jackets or sweaters versus the higher bar in the closet. Hang a bar lower in the closet, too. Those in-closet shelving units are wonderful and save space in a bedroom (no dresser needed) that could be tight if a wheelchair is needed. We have those shelving units in the guest cottage as well as ds's bedroom closet and our spare guest room, in the main house.
Lighting, lighting, lighting!! Multiple switches so the person doesn't need to go back and forth to turn lights on or off. Better to have a central switch on either end of the largest room near the bathroom and bedroom. Extra electrical outlets near the bed (on a separate breaker would be great, in case an electric bed is needed).
By the way, I was wheelchair-bound for 10 weeks last year and managed beautifully in our home. We designed it so that we could always live here, and we discovered how well we had designed earlier than we expected!! We have also had a friend that has MS, and is in a wheelchair, stay in our guest cottage and she gave it a huge
, saying it was better than any hotels she's ever stayed in!
I'm sure there is more stuff, but I am off to the city. We're renovating my Dad's house to sell (he died in November). 180 miles, roundtrip, today! I'll check-in later.
Feel free to pm me if you want any additional ideas. I'm really experienced with this stuff!