When I was first married (34 years ago) there was a boat rental at Big Bear that was in Boulder Bay and they had some 18 foot Jon boats that they had built a small plywood "cabin" on up near the bow. My wife loved those as she could get out of the sun and wind etc. I don't think they've had them for very long after that. In fact, I don't even know if there a boat rental there now. It's been a while.
A buddy in my bass club has really nice Ranger fish and ski, very fishable and he does well- the non boaters in our club love fishing out of that boat- especially when it's cold or long runs are necessary, like an early morning run at Havasu or the Delta. Probably not the cheapest option, but if you have a little cash and don't feel like kicking your girl to the curb as others have suggested, check it out. LOL
get the adjustable bimini top, bbq, and ya a deck in the back to lay out on. I did that for mine, she loves it. oh don't forget the minn kota 101 on the bow too.
Quit fishing!
Oops...My bad! Young man the first and most critical chose you need to make is....Am I going to just Test Drive or Buy the Girlfriend Thing! Next....Plan on a family? Once you make the single most important choice of your young life then....And only then....Do you try to decide on what would make that relationship the happiest it can be for the long haul. Choose Wisely Young Man ... Your only young Once. Good Luck!
As others have said the fish/ski option may appeal to the GF but depending on your style of fishing it may not be optimum for you. I've got a Ranger Z21 (huge bow platform) and my GF who doesn't fish enjoys just relaxing on the back with her own beach chair that has an umbrella attached. This works out for me as I don't have to worry about possibly snagging a bimini top when casting. So, depending on what your budget is there are several options to pick from.