I did laundry by hand for years and years, though I upgraded to a machine a couple of years ago.
Washing in cold water is depressing, unless it's a very hot day. Your hands get cold, and eventually numb. Warm water is much better psychologically and I suspect also for loosening the dirt and grime. On a sunny day it might be possible to rig up a hose-pipe with a spray nozzle that you can switch off, leave it lying in the sun, then you might have enough warm water from it to fill the laundry tub without having to actively heat water. It doesn't have to be very hot - just enough to make the experience pleasant rather than something you come to dread.
I found it was essential to have the tub set up at an appropriate height so that I never had to bend. If I got the height of both the bench and the tub right, it would be an awesome workout to strengthen my arms and back without ever straining anything or making me ache.
Also, soaking is your friend as is loosens the dirt without any extra effort. Put the stuff in a tub with soapy water (can be cold...) and leave it for an hour or more while you do something else. Then change the water and you'll find that most of the dirt goes straight out in that first lot of dirty water.
Here's a photo of my old set-up...
I used two builders' trugs, one with holes cut in the bottom for drainage so I could put wet clothes in there to let them drain after scrubbing them, then they could be put back into the other tub for rinsing.
I never wrung the wet clothes out, but I had a covered area I could hang them to drip dry and then if necessary during cold weather I could bring them indoors to finish drying.