Have been reading this thread with interest.
Thinking at this stage I might stick with my current method. Which is about as simple as it gets.
My camp shower is just a bucket with a lid and a scoop. Inside the bucket I keep whatever I need for my shower (to suds up with, and a flannel). I take those out of the bucket, place them on the lid and place on the ground (so it serves as a little table top for my stuff, and they don't get dirty).
That leaves me with the bucket, which I fill with water. Then I take a pot full of water out of the bucket, boil it on the stove, and pour it back into the bucket. That seems to give me the perfect temperature, just about every time. But if it needs a bit more I can always do it again. Takes less than 5 mins.
Anyway, then the scoop is used to tip over myself, I lather up, then the scoop again to rinse.
My 10L shower always seems to leave a few litres at the end, not needed (strictly speaking) but absolutely lovely to up-end directly from the bucket over my head to finish off.
It's the way a lot of people shower in India, but using the hot and cold water tap in the bathroom (at bucket level). I picked it up as a method on a visit there a few years back.
It's amazing how nice a shower method this is. And no issues about pumps, pressure, hoses or anything like that. So long as you have somewhere to boil a pot of water, you're all set
P.S. No doubt this has been mentioned before, but in my quick flick through the thread I couldn't see it, so thought I'd mention it just in case.