I can run 27x1-1/4" @ about 70psi no problem, but I'm pretty light. Need to check PSI before every ride, also, make sure they're aired up.

I'd try to go 700c if you're gonna get some new wheels. Take a look at your brakes to see if your brake pads have enough adjustment to go 4mm lower, maybe consider filing the slots out a bit if they're close but no cigar.

Then you need to figure out the rear spacing of your frame. Probably 120mm or 126mm.

If 126mm,
Velomine has black rim 126mm super cheap, $95 a pair. Silver rim @ $120.

If 120mm call and ask if they'll respace/redish as needed.