IMHO, thigh pockets are entirely inappropriate for sidemount diving. There are a couple of known solutions for this;
1. Sidemount Butt Pocket. These are sold by a variety of sidemount manufacturers. They utilize the optimal space at the back of the sidemounter, clipping to rear D-rings via two double-ender boltsnaps. Good sidemount training courses include skills/drills to fetch the pocket, remove/replace necessary objects and return the pocket to it's proper location.
A LIST OF SIDEMOUNT POUCHES YOU CAN PURCHASE
2. Chest Mounted Suit Pocket. If you can put pockets on your thighs, you can put them elsewhere. Don your sidemount rig... see where you've got free space on your torso in an accessible location. Get a suitably sized, streamlined pocket fitted there.
3. Waterproof Notebook. Abandon the bulkier, traditional wetnotes and get a small-sized waterproof notebook. This can be stored in a flat pocket sewn onto an exposure suit arm or even tucked/clipped (
small bolt-snap) beneath wrist slates etc. I used these when I was in the military (they were issued) and I had a small box of them for diving use over the last 10 years... they work great. I use them in conunction with wrist slates... I put my deco plans and contingencies on the slates (
permanent - sharpie on duct tape)... and I use the small notebook for any recordings or messages I need to make on the dive. The notebook also allows me to tear off pages if I need to pass on a message (
i.e. left on a guideline or sent up with a DSMB to surface support).
example: Silvine Waterproof Notebook
4. Cylinder Pocket. Use existing, or extra, cam bands on the cylinder to attach a belt-secured type pocket. The sort of pocket you'd normally fit to a harness 2" waist strap. FAR from optimal for technical/overhead diving, as per putting weights on your cylinders...but workable for recreational, open-water sidemount divers (who aren't 'beginning with the end in mind').