The combination of a box spring bed and a waterbed seems to me to be the ideal solution. On the one hand because of the ease of getting in, and on the other hand because of the comfort of the mattress. If the water mattress also contains damping fleece, which reduces rocking back and forth and optimizes filling according to body weight, nothing stands in the way of sweet dreams. However, these things can be really expensive.
OT:
A little anecdote on the side. I once told the wife of a colleague that she could not use a waterbed because the water connection for hot and cold water was missing in the bedroom. When she asked what a connection was needed for, I replied, well, hot water for winter, cold water for summer.
A few weeks later, when we were out together, we passed a specialty bed store. She wanted to get some information, so far so good. After a while, the specialist salesman came up to her and asked what she was looking for since she had been bending down and walking around the beds constantly.
Well, she said to the salesman that she wanted to see where the water connection for the pipes was so that it could be properly installed at home.
Can you imagine the face of the salesman? Well, I stayed out of it. Nevertheless, the laughter was loud and I had to listen to quite a bit.