Loose fit might be fine, Andiamo is a maker of liner shorts with crotch padding,
but they are priced about the same as some as cheap Lycra nylon shorts.

saddles with the cut out in the middle would present less of an issue with the thick center seam on most denim trousers.

I got 2 pair of cheap charity store gaberdine pants ,and had a local alterations sewing shop taper the legs, keep em out of the chain, and double the seat and they are a good alternative..