I've had both low BP and low temp my entire life. Neither one is, by itself, a bad thing - in fact, it's usually a good thing, if anything at all. However . . . .
The numbness is much more likely to be a result of peripheral neuropathy, or problems with the nerves in your extremities. It's called paresthesia (plural paresthesiae), and it can be one of the most uncomfortable, worrisome symptoms of autoimmune illnesses. In fact, it was the fact that all four extremities went numb when I slept - whether I slept for 10 hours or 10 minutes - that finally drove me to the doctor, although it was still years before I received any kind of real DX. The paresthesiae don't result from low BP/temp, although if you have circulation problems generally, I imagine that low temp would aggravate it. They probably were initially triggered by whatever initially triggered your fibro symptoms. In my case, I clearly had this since adolescence, at least, but the trigger that blew my symptoms wide open was the flu vaccine. Incidentally, think back over your vaccination history - if you had a flu vaccine just before the onset or serious worsenings of your FMS symptoms, tell your doctor.
As far as dealing with the numbness goes, I haven't found anything that really works. I've gotten so accustomed to it that I can now mostly ignore it - at least, in comparison to the pain and fatigue!
Anyway, hope this helps. All of this is something to take to your doctor - s/he should be reassuring you on the paresthesiae and explaining how it's caused and what to expect. If not,maybe it's time for a new rheumatologist (I went through I don't know how many specialists before I found one who took me seriously).