Sometimes, the shuffle works against you. However, if these were NEW packs you mixed in, the chances are that the monsters were clumped, because that's frequently how they come from the factory (it's an artifact of how we export the files). Always shuffle new
Munchkin games and expansions thoroughly before playing.
There are a couple of ways to mitigate the "not seeing enough monsters" problem. The one I always recommend, especially when you're playing with multiple sets and/or expansions, is to use the "Listening at the Door" faster play rule on p. 6 of every
Munchkin core game. You're guaranteed to see two Doors every turn and if you aren't facing monsters, you also get a Treasure - so it doesn't feel like you're totally stagnant. It's not a HUGE change but it does increase the odds that you can Look for Trouble.
As for the Deluxe board, we have you covered: check out the
Level Playing Field. It's sized to fit inside a regular
Munchkin box and even comes with extra cards. (Or, if Christmas is your thing, try the
Yule Log instead.)