Yep..thick leggings should do it..Primark are a good source of cheap stretchy bottoms .. My first lesson I didn't have any chaps and got badly bruised from the stirrup leathers so really worth getting some half chaps to wear.
I don't wear jodhpurs for riding, I wear stretchy jeggings and I have a pair of long waterproof leather boots which I stretched and worn in to fit over them. I'll be going to my first show in two weeks so will wear some jodhpurs then. Means I can pop into supermarket on the way home without feeling self concious lol
Be careful in leggings.
The first few times I was on a horse they were in my favourite leggings..
Sadly, I had to throw them out due to holes all along the inside seams.
Jeans rub, but leggings rub away and deteriorate.
They're okay for one lesson but make sure they're thick and not expensive.