[bengal-stripe]

Most trousers will lack sufficient material in their seams to let out the thighs significantly, but you can but look & ask!

Most trousers have in the "fork" (the bit between your legs) additional material to be let out. Look inside the trousers onto the inside seam, just before the two leg seams join.:

Usually the back section has excessive inlay, something like 1 ½ ins. That is there to be let out, if necessary, giving about an extra inch more room around the op of the thighs.

Whether or not that is sufficient in your case, you'll have to decide.