My experience is that the armrests between the two seats on the CRJ are easily raisable. The only exception in general is the bulkheads and emergency exit rows (I tend to go for these being a tall guy); most of these seem to be fixed, and the seats are particularly narrow.

I would also say the first class seats on the regional jets are smaller than the FC seats on mainline aircraft, so they may not be large enough for you to be comfortable.