I'm devoted to Old Navy's boyfriend denim shorts. I have 3 pairs. I have what I call "athlete thighs." And 2 knee reconstructions with intense physical therapy. My thighs are rock solid muscle and will never be called skinny. These shorts are comfortably roomy in the thighs.

http://oldnavy.gap.com/browse/product.do?cid=1009256&pcid=35158&vid=1&pid=506476042

Or get a pair of jeans that are fit comfortably on your thighs and have them made into shorts.

You could size up and then have the waist taken in -- it's fairly easy to do and not too expensive. It could be about $20 last time and it works really, really well.

Honestly, OP, I feel just like you and do not want stretchy material in the hot summer. I stick to fluid shorts, and that basically takes denim out of the equation. This summer, you can find fluid chambray shorts.

Chambray would probably be the closest..

http://www.gap.com/browse/product.do?cid=1032109&vid=1&pid=790352002

https://factory.jcrew.com/p/womens-clothing/shorts/solid/5-chambray-short/B9356

I'm late 30s, in good shape, size 0/2. I have a very long torso, and normal size thighs for my body -- the end result being that I do not have the super long stick thighs with a 6 inch thigh gap. So when I wear most denim shorts, they squeeze around my thighs -- and then end result is not a flattering look. Basically providing a tight horizontal stripe at the widest part of your thigh. I am of the oldschool mind set that wearing something slightly loose is more flattering.

I can't just size up, because then the waist is way to big and the shorts sit too low on my hips - now creating a big horizontal stripe across the widest point in my whole body. And I need the shorts to be pretty short-short, because my long torso/short legs look terrible with longer shorts.

Old Navy chino pixie shorts http://oldnavy.gap.com/browse/product.do?cid=1009253&pcid=35158&vid=1&pid=769594022 work well because they have a little extra space in the thigh (almost like a slight flare), but they don't come in denim. So before you launch into "shorts are just unflattering" -- it's not true! There are non-denim short shorts that look great on me.

Denim shorts, much like jeans generally lately, seem to only come in super stretchy material that is intended to fit snugly. Anyone have any ideas for denim shorts that have a little more room in the thighs?