I sit on a stool to have a shower myself.
I have an energy and tangle-saving technique for washing my hair, which is long.
I start by combing it all forwards over my head, upside down.
Then I wet it.
I get hold of the shampoo bottle, and spread a thin line of it along my hand,
then apply that along the back of my head,
then I gently massage it over forwards, towards the front, getting the shampoo right through it - without tangling it.
I prop my elbows on my knees and drop my head forwards to reach my hands, so there is no real arm-raising involved.
Once the shampoo is through my hair, I bundle it up on top of my head to "soak" in the shampoo, while I get on with washing the rest of myself.
I use a long loofah to clean my back (and other places).
I've found that only showering once a week means I do need to "exfoliate", the loofah is good for that.
After rinsing the shampoo out, I put the conditioner on the ends and throw the lot backwards over my head, which gets that through it all - most at the ends and least at the roots. I use a wide toothed comb again to completely detangle, while the conditioner is on it, then rinse and wrap it in a towel "turban" to dry it.
To dry myself, I put on a towelling bathrobe and my hair in a towel, while I get on with dealing with cutting toenails and other post-shower stuff. I just turn the hairdryer onto any bits of me that that are still damp after a while in the robe.
It's too much after the washing and the humidity to try to dry myself with a towel.
Sitting on a stool and
propping your elbows on your knees does mean you do a lot less arm raising stuff - and most of you is reasonably accessible from this position.
I do recommend strongly that you rinse your bum after soaping it and
before trying to sit down again - I've gone sliding around the bath on a few occassions.
A very general, but incredibly important everyday energy saving thing is always, always, to have your feet raised if you are sitting.
This goes along with the general - "never stand when you can sit, never sit when you can lie down" stuff.
Knowing why helps!
It saves your heart from doing a huge amount of extra work.
Your heart has to pump
all of your blood around
all of your body.
Not only does your heart have to get the blood down to your feet, it has to get it back up your legs again - and that is against gravity - and very, very far away from the source of the pumping - the heart.
When you are walking around, the muscles in your legs squeeze the blood vessels and help your heart push the blood back up again.
(So never stand still either - if you must stand, shuffle around a bit.)
If you are sitting with your feet raised, you are removing the effects of gravity from the work your heart has to do. Bringing your body into a reclining position as well, will keep everything as easy as possible for your heart to do its job.
Your blood vessels will all be level with your heart, it will only need to push the blood along, not up and down as well.