if your clothing has fit well up until now, maybe you want to try something like Body Glide before changing anything else? Did you notice your breeches having loosened as you rode or did you get wet from sweat or rain during the ride?
I ride in my normal bikini-cut underwear, yoga tights, and cotton crew socks at home and can do so comfortably for up to about 25 miles (the farthest I go at home). At competitions, I change to boy shorts that stop a few inches above my knees and compression socks under my tights, and apply body glide from ankles to crotch, taking care to get my thigh pits (good term!) thoroughly. So far, that has solved any issues I have had with rubbing unless I get soaked and have to ride that way for many miles before being able to change (and honestly, I am not sure any clothing on earth would help that for me).
Would padding create additional bulk that would only make more rubs? Something you may try would be pantyhose under your breeches - I know several endurance riders who do this and they say they have no issues with heat.