you can just get a set of textile or mesh riding pants that will offer abbrasion protection. you can get overpants so you can just slip them on and off. much more convenient. you could also get a set of kevlar-reinforced jeans (draggin jeans and other brands), or even abrasion resistant tights to wear under your pants.
denim offers basically no abrasion protection when you hit the ground. leather pants/full on leather riding suit goes to the opposite end of the spectrum, and is really overkill for everyday riding. then again, that other kind of safety gear is expensive.
check places like newengough.com, revzilla, etc. these things all fit weirdly, as they are made specifically to be worn in riding positions, so itd be to your advantage to go somewhere and try your safety gear on first. unless youre just getting the jeans or shorts or whatever.