Slightly increased “bad guys” activity should throw a challenge. Having to fight three undead hordes in a row, with equipment getting damaged and wounds piling up would give you second thoughts about it.
Even at early start having more patrols and attacks to towns could definitely add some spice on top of having to heal and repair over time.
Getting trapped as I was by a deadly horde ( glitched trying to cross a bridge ) was pretty brutal and fought to the very last breath. Eventually the numbers could tell. And eventually I didn’t even got my assassin close to the necromancer.