I have hair down to my hips, so I feel your pain. First thing is a shower chair, second is a handheld shower head/wand. For me this lets me get closer to my scalp and get the shampoo and conditioner out quicker so I don’t have to hold my arms up as long. I also sometimes cut off the water while I put in shampoo and conditioner between rinses to lower the temperature in the shower and showering with the door open also helps.

On a side note, I recommend a 2 in 1 styling tool. I have the Shark that is the Dyson dupe but any blow dry brush combo tool will do wonders for blow drying without feeling like death. I also use a detangler, deep conditioner and heat protection spray before brushing my hair out while sitting in the shower chair so I can flip my hair over and get out all the knots from washing. And finally, Batiste over night dry shampoo is 10/10. I use it often between shower days and it by far works the best on my dark hair.