Comfy shorts for dresses

I have loved wearing dresses. I am just more comfortable. Going back to teaching I am planning on wearing comfy dresses a lot when I’m not allowed to wear jeans. I like to wear shorts under my dresses. I just feel more comfortable and professional especially when I’m walking around. I used to wear spandex or bike short type shorts. I cannot find anything like that for maternity. Everything I find is super tight and my usual shorts can’t fit. What have you used before or found that doesn’t break the bank?