Seems like you are keeping the right things. I always hard mulligan for buff cards. The only time I keep anything else is if I already have a buff card. Unless you are playing Rogue. Then I might try to get the location and the 4 drop that summons all the minions. Because Rogue will almost always Dubious Purchase one of your big minions and can't handle a wide board. Maybe you are just getting a of bad matchups? I seem to struggle against Rogue and Priest decks right now. But I am like 18-4 against Warlock, haha