I can't add actual real world recommendations, however, Dometic may have what you need. They have 2 cassette style toilet product lines, the 960 Series and the 970 series. I didn't dig too deep, but it appears that the 960 Series is the traditional bellows style flush system, whereas the 970 uses a pressure style flush. It appears that there is a way to pump up the pressure in the fresh water tank so that when you go to flush you simply press a button and the pressure forces the flush to happen. So that may be the best of both worlds, a single button press to flush, but no batteries.
Also, they have several different toilets in each series, of varying sizes and capacities.
Again, I can't speak to real world performance, but there are specs and very thorough user manuals for each variant of the toilets. Just may be an alternate route for you to research.