A small US company called "Smoothstride" makes the very best riding pants I have ever worn. They aren't breeches in the English sense. They are boot cut and look like pants , basically, but have a fake suede full seat and stretch so nicely that the are great for larger women. I wear a size 16 to 18 and smoothstride trail rider pants fit me perfectly.
Dragon: They're not cheap, but Irideon makes some very nice winter pants. You would probably fit in their XL size. They do make plus sizes in 1x-3x, but at a 36, the regular XL would probably be just fine.
Also, I buy thermal tights from Academy Sports and have really had good luck with them this year. They're cheap too, only about $15 a pair for the smooth/soft type. The waffle type material doesn't work under breeches very well, lol.