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.
Dometic Toilets