Can't get ambient temps high enough!

[Lolo76]

I've been trying for MONTHS to get my temps perfect, ever since I moved to a new neighborhood (in February) with a different climate... it's pretty cool throughout this whole area, but my new place is ridiculously mild all year. Our outside temps don't get much above 60 even/especially in the summer, and don't drop below 50 too often either. Great for me, but the snakes are probably getting a bit chilly.

I use racks with flexwatt, thermostats, Acu-rites, and the whole shebang - one of the racks has back heat, though, so it's hard to measure the hot spot there. It's mostly housing corn snakes, who don't like it too warm anyway, although I do have 3 BPs in there as well. But no matter what I do, the ambient temperatures won't get above 74-75 degrees in any of the racks. Hot spots are also a bit low, but much closer to ideal at 86-90 depending on the tub/rack. I tried turning up the thermostats to 97-98, and the hot sides were getting too high, with very little change to the ambient.

So when you live in such a cool climate, how do you raise the ambient temps safely? They're kept in my bedroom upstairs, which is one of the warmest spots in the house... and I can't turn up the house's heat much more, without baking the humans & paying $300/mo for utilities. Any ideas? Should I maybe add a few heat lamps? I thought about a space heater, but as I mentioned they share my bedroom - I'm not so keen on sleeping in 80 degree temps myself. And since I do have a roommate, there's not really anywhere else I can put them (except the living room which is frigidly cold 24/7). They do seem fine, however, and I've never noticed any signs of RI or discomfort. In fact a few of them still hang out on the cool side, like the Mojave who'll move his hide to the cool end every few days. I am concerned though, and would like things to be perfect!