When the temps drop in autumn (below 50 in the morning) I switch to liners under long workout pants.
Under:
https://www.rei.com/product/170782/z...B&gclsrc=aw.ds
Over:
https://www.rei.com/product/157092/r...ing-pants-mens
Not cheap, but I've gotten 3 seasons out of 2 pair of liners and 2 pair of pants riding appx. 150-200 miles a week. And, they keep me warm down into the high 30's with a merino wool top and light jacket.