You can buy inserts which go on the legs of the glasses. They are supposed to spread the clamping load of the headset and avoid the pressure point where the glasses press against your head - maybe somebody on here has tried these and can comment further?
I've used the Sennheiser HME100 passive headset (with the 'second edition' soft earcups) in a PA-28 for about 3 years and never had a problem. My glasses have 3mm diameter legs and I always got headaches with DC gear due to the high clamping pressure, but it very much depends on the shape of your head. I'd recommend that if you are buying another headset, go to one of the shops and take a very long time trying them on.
If you 'get on' with passive David Clarkes, Peltor or Pilot, you could always have an ANR conversion done at a later stage - this costs about £180 and reviews of such modifications have been very good.
Headsets are very personal things which need to fit properly, so don't go buying Sennheiser because I say they are great - or DC's coz others think they are the best bet. Look for weight, clamping pressure, comfort and quality then choose which set is best for you.
Good luck!