I am working on a list of nonmagic items for you to be able to buy. I don't generally like house rules (with the exception of monsters, which I often make up, as you've probably noticed) and I suppose I've made a few magic items... but I feel 5e really dropped the ball with stuff to buy. I mean, they resisted the idea of people buying magic items, but then never made much else for you to buy either. I'm working on a list I call "superior items" - just slightly better than regular ones, made by master craftsmen. I think low-tier this is what people should be buying before you even get too many magic items.
The mounted crossbow can be like that. It has +5 to hit, or your own crossbow skill (if it's better) and does 2d6+3 damage. It's got a nice big crank to load, and a rack of quarrels on top, so it's just as fast as any smaller crossbow to load.