I use Tesco tubes (24", £1.97 at last check I think) and run 30-35psi and only occasionally pinch (2.4" Holy Rollers). What tyres you running?
Options I can see are: slime tubes or slime to seal the tube once pinched (not sure how well that works with trials pinches as opposed to thorns etc.), running tyres with thicker sidewalls (Kenda blue grooves may be heavy but you can run them at about 10psi and still not pinch), running fatboy DH tubes or at a push running a second tube, slit around it's internal surface, wrapped over the new tube to try and increase protection (with a bit of talc thrown in for good measure). Riding more good would definitely help though .