My thighs are large too
Can you sew? Knickers are so easy to make. My favourites are by kwik sew. It is an old pattern, there are very many knicker sewing patterns and instructions on youtube, you can use any pretty stretchy cotton fabric and trim with stretchy lace
If you have even minimum sewing ability, you can make the legs wider ie a size bigger and then just grade to your waist size
A nice loose zig zag for sewing stretchy lace and not stretching as you sew and you would achieve the result you want