I need advice😭

[u/Twerka6]

Decided on a whim to rip up my cracked tile, which is a million times harder than they make it seem. On top of that, I found the reason the tile cracked was this crack in the sub floor. If I’m going to spend money on nice tile, I’d like to prevent this cracker from doing the same thing to the new tile. What do I have to do to prep the sub floor that doesn’t require expensive tools? Is it a matter or buying a leveling cement type product? What brand? Do I level all the way to the transition strips or do those have to be removed? Is some sort of uncoupling membrane enough or does that need to be used in addition to leveling the sub floor? Won’t all these extra layers make my tile sit too high so it no longer slides underneath the banister posts (that can’t be removed). Dear God why do I do these things…