Look around for an ex-RAF Mk4 helmet. You can buy an adapter but I replaced the dynamic microphones (on both the boom and oxy-mask) with electrets and put variable resistors in the earcups - quite easy to do and means it works with GA radios without any external gizzmos, plus can easily be reverted for mil types.
Whichever type you opt for remember to have a quick disconnect near the helmet if you wear a parachute!
HFD