Is there any ballpark for what temperature range is comfortable for
cats?  I prefer it cooler then most people, 17-18 degrees is about right
for me, but when my girlfriend is home we usually have the temperature
up to 22 or 23.

In the 17-18 range I'm noticing that they tend to be more hyper then the
18-20 range, chasing each other, fighting, playing with toys, etc.

Any cooler then 17 and the cats act like they're cold, they insist on
snuggling with me, pressing as much of their body against me as possible
(which is different from how they normally curl up to sleep on me).  If
I won't let them cuddle (or won't sit down so that they can cuddle) they
meow at me until I turn up the heat.  Fair enough, I get the message.

I'm curious, when the house gets to 16 degrees (which it does at night
sometimes), is it too cold for them?  I tried keeping one room warmer,
but they didn't seem to spend any extra time there.

Part of the reason I'm curious, my girlfriend will be moving out
shortly, after which time I expect it will generally be cooler in the
house then it is now.  I'm debating whether I should keep it warmer for
them (or at least keep a room or two warmer), or get an electric blanket
or something for them.

Unfortunately they can't sleep with me at night -- My g/f is slightly
allergic and she can't sleep if the cats shed all over the bed.  Once
she leaves, I might consider leaving the door open so the cats can come
sleep with me, but that will only work until I get a roommate, once I
get a roommate I'll need to close the door at night, and I don't think
the cats will want to be cooped up in my bedroom (I have a huge house,
but I'll use the smallest bedroom for me, there is no chance of putting
a litterbox in there, nor food or water) -- I'm thinking that it's
probably better to not let them get used to sleeping with me since I'll
have to put a stop to it down the road, the last thing I need is a cat
scratching and howling at my door all night long.

Thoughts?