Only a suggestion, but I haven't had a flop and I've spent a fair bit on certain players, I always make sure I have very good scouts and then check that the personality of the player fits in with the team. It seems to work for me.
I play that formation but with 2 CMs instead of 1 DM and 1 CM. just put one to support CM and the other to ball winner and more defensive. It means the midfield isn't as thinned out and you don't lose possession as much in the middle. try that.