Just bought a Alpinestars KMX-9 V2 SUIT and it’s a little snug in the waist and under the shoulders.
Unfortunately cannot go larger as the arms and legs are already a tad too big.
What other suits if similar quality should I be looking at that have a roomier fit around the waist and shoulders?
Some suit models will have built in stretch panels around places like shoulders and lower back. The idea is when sitting in the clam-shell position, with your arms extended, the suit can move with you without sacrificing a good fit. The panels are covered by slide-resistant material, so you are still protected. Other features could be mesh sections for better ventilation and waist & neck belts.
This might offer some insight on comparisons:
I have an AS suit also, I do find they’re baggy in the arms and legs but tight on the shoulders. My Sparco is much better proportionately