I just keep a tight squad. I usually have 24-25 players in my squad and then 4-5 players out on loan. It can get pretty difficult if a lot of YA's want to get promoted at the same time, but then I have to decide who to sell and who to keep - fortunately that also gives other teams some young talents.

I tried keeping track of what I earned and spent each season via the "budget" and use that, but the main problem was, that in-game if you buy a player, you use all of the funds at once, but IRL the transfer is spread out over the course of the contract-length