renovating unlevel rooms

I have a charming 1923 bungalow that needs some updating in the kitchen/baths. Unfortunately, the floors and ceilings are not exactly level (and I don't have the thousands I would need to correct that problem). It was built by my next door neighbor's grandfather, who was a minister, and lots of rooms aren't exactly square. I've been told that putting down a tile floor on a sloping floor would cause the tile to crack, and there's also the issue in the bathroom of a toilet that is slightly pitched forward, as is the sink, caused by the slanted floor. Can I put something on the subfloor when I pull off the old linoleum to level the floor a bit...or will everything then seem more off-kilter since the ceiling also slopes? Thanks, Kirsten