You could level the entire bathroom floor with self-leveling cement (slc). The stuff isn't cheap, but you may not need all that much. You need to really understand how that stuff works, or you'll end up with an expensive mess. Check out www.johnbridge.com for tiling, slc, and more help. It's SO much easier setting tile on a truely flat floor, and level makes it easier with the toilet and vanity, too. I've only used SLC once (and I used Ardex K-15), but many people swear by some other brands. Keep in mind that as soon as water hits the stuff, you only have minutes to mix it and pour it. It's not like dealing with concrete - you really can't tool it as it's more like pancake batter that will run everywhere it isn't contained. It goes from powder to liquid when mixed with the water to hard as a rock in often less than 10-15 minutes (and most have you mixing for about 3 of those minutes), so you need to understand what's going on and do it right the first time. I mixed and poured 8-bags in about 15-minutes, keeping the wet edge to keep things flowing, but it took a lot of prep - premeasured water, bags opened, lined up ready to pour into the mixing barrel. You really want help doing this - you usually mix two bags at once (100#), plus the water (probably another 50#), and the barrel - it's HEAVY. You need to carry it to where you will be pouring it. I won't do it again without help, preferably at least a couple of people - one to be mixing, while two carry and do any feathering, if required. Think about the chocolate that you may get your ice cream cone dipped in...liquid one moment, hard as a rock then next. It's not quite that bad, but again, you don't have much time to mess with it. It does self-level, but like a pancake in the pan, it won't go to a feather edge unless you help it out by spreading it. It's easier to have too much and let it be deep, than not enough and not get enough time to feather the edges before it starts to set. If you go this route, follow the instructions to the letter and that always requires buying the brand specific primer.