The upper west side is pretty good...
In my opinion though, you're in NY for only a limited amount of time, might as well make the best of it. Midtown is terrible. Avoid at all costs. Unless you're going on some night missions, but let's face it, you will be there with your girl so that's not happening.
Focus your efforts below 23rd st. Yeah, doing things like going uptown to check out Harlem are worth it, definitely, but you probably don't want that to be your home base. Yeah okay it's not super hood like it used to be or in the movies but it's out of the way from where you'll spend most of your time and if you're not a resident and you don't know where youre going it can not be the best place to be caught slipping at night, on your way home, with a girl.
I guess I'd have to say, I really recommend checking out some options in Chinatown. It is a pretty interesting place, and really what's more is that it's surrounded by areas where there is an abundance of good places to eat, drink, go out, skate, etc, and it won't be extravagantly expensive, unlike soho, west village, even east village. I'm partial to the east side, as that is where I reside, but it can probably get expensive on the temporary room front, too. Another benefit regarding Chinatown, if you have a relatively small window of time, like your girl wants to take a nap for an hour or two, you can be at the LES park in less than 10 min and get to skate a sick park. Look, I don't know her or how chill she may/may not be, but I know how trips with the girlfriend go, and most likely you will have to squeeze in skating around every last other activity. *** which makes me think...a lot of bicycle shops in manhattan rent bikes. "exploring certain areas on ground level", meaning dropping something like $20 on a 24 bike rental, may get you on your board, stumble on a few spots, and keep her happy and none the wiser.
The only really legit skate shop in Manhattan at this time is a relatively new one called Labor, which is also, coincidentally, located on Canal st...in Chinatown. Nice ass dude runs it, which, in my opinion, directly contributes to how chill other people you may run into there are. Asking people to recommend things in person is always the best way to do it (about spots, restaurants, directions, whatever). Yeah, cool, DQM is the best place to buy shoes, definitely, and I don't know if your fashion sensibilities would lead you to Supreme or not, but Labor is the skate shop to check out.