My Guilty Pleasure -- Obliterated

OK, the situation is not so dire as the word obliterated makes it sound! It's just that I really enjoy using certain words, so please indulge me this time.

What is my most guilty pleasure,you may ask? Well... it should be a pretty simple thing, in practice, however, it can get rather tricky for various reasons I shall soon outline.

My most guilty pleasure is to waste vast quantities of water and electricity and take extra-long, extra-hot showers. I feel extra-guilty for the wastefulness, but oh, I enjoy it so, so much! I feel relaxed, finally truly warm (I'm always cold) and it's wonderful before going to bed or, alternately, on a beautiful sunny morning when I don't have to rush out the door to go somewhere.

Except that... I haven't enjoyed my showers at all ever since we moved to this house. In the summer it wasn't that bad, but now in the winter it's just awful (even when we turn the heat up high and try to trap it inside the bathroom).

The culprit is the shower handle or knob. We have the simplest kind, more or less like this:









This knob only turns the water on and off. Colder to the right, warmer to the left. It does not come forward or up or down for INTENSITY of water output.
Tangent: Oh, and those of you who have lived in the U.S. all your lives may not have thought about it, but here one can find so many different kinds of shower handles, it's maddening! I had never thought of it until many years ago in Brazil when I read my aunt's journals from her two trips to the U.S. back in the late 80s, early 90s. She described in detail how each hotel bathroom shower knob worked and I think that at least in one occasion they had to take a bath because they couldn't figure out how to get the shower to work!

In any case, if only our shower handle were like the one on the left, or even if there were three handles as there were in our old house (one for hot water, one for cold, one for shower/bathtub spout) and I could control the water intensity, then I could have less water and the water would remain warmer during the whole bath.

Obviously the real culprit is having a hot-water heater that has a tank and thus, a very limited amount of hot water. Another solution, since our kids are older and generally more careful, would be to increase the water temperature in the heater, but we were unable to find the panel to make that change (and plus, this is a rental house and we can't risk breaking anything, so definitely replacing the knob is not an option).
I have to confess that I was utterly spoiled by the on-demand water heater (that was powered by an oil furnace -- our house had hot water baseboard heating) we had in our old house, but I don't remember having this problem at our two previous houses either. :(

Needless to say, I'm looking very careful at every shower knob in all the houses we're considering buying. Ideally, it would be nice to be able to install an on-demand water heater in our future house someday. Meanwhile,  I will keep dreaming of hot long showers. At my parents house these showers are the best because their water is heated by solar panels (physically heated, they don't gather electricity, it's just a problem on cloudy days when a regular and expensive electric heated has to be turned on).

P.S. One problem I almost neglected to mention is that when I say hot showers I mean scalding hot because my body can withstand very hot water. For many years when I was going up my mom used hydrotherapic (water based) treatments to help me with my asthma and allergies, so I took countless hot baths in which the water was made hotter and hotter until I was sweaty and couldn't take it anymore, so I can stand (and really enjoy) truly hot water. :(