I'm very allergic to cats, and we have 6.
I get hives, runny/red/itchy eyes, nose, sneezing... any accidental scratch turns into a HUGE red welt... but with meds and dust/dander management, I don't suffer any of that (except the red welts when accidentally scratched, which, quite frankly, happens a lot because we pet, pick up, and play with the kitties all the time).
When you (or your girlfriend) get a kitty, even though it's REALLY hard, do not let kitty in the bedroom. That should be off limits. That in and of itself will really help.
I take Zyrtec-D 2x a day, and I have an albuterol inhaler for when I have a problem. I have Ultravete steroid cream for when I get hives. They're all prescription and thankfully insurance pays (mostly) for them.
We vacuum a LOT. I've hung blankets over the backs of the lounge chairs and couches - that's where the kitties seem to like to hang out the best. I fold them up when I'm using the couch or chairs (or when we have company over), and I wash them weekly. It helps cut down on the vacuuming time.
Wood floors vs. carpeted help a lot (something to think about when you move if you're already in a carpeted place).
We have an air filter of some type in every room. We vacuum the filters weekly and replace them every few months (or as needed).
Because we let the kitties in the bedroom (we lived in an RV when we first rescued cats, so there was really no way to NOT let them in the bedroom, lol!), we have a Frederick's air filter. They're really expensive but it is INCREDIBLE and really quiet (just large!)
I know there are some people that get allergy shots - those should work too, and would be easier than taking a pill once or twice a day.
We brush the kitties a lot - at least daily - with one of those grooming brushes that really gets the hair out (they were scared of brushes at first, of course, but they have ALL come to love them, and practically fight over being brushed, lol!). This really cuts down on the amount of hair (and thus dander, which is my problem) floating around here.
Ummm.... Blinds are easier than drapes. They don't catch the dust/dander. We have drapes in most of the windows though, so it's lots of vacuuming...
...and... that's all I can think of right now!