I’ve got a simple modification I use randomly in several of my kayaks (I have a rather hoarder-worthy fleet at the moment) that helps with leg comfort. I have half of an old 1/2" thick Ensolite pad I used to use under my sleeping bag for backpacking – the cut piece is 24" wide and about 36" long. A closed cell foam yoga pad would work as well. I stuff that into the cockpit over the seat and fold under the edge that faces the bow once or twice so it adds just a little padding and elevation under my thighs. This also enables a snugger fit without cramping and adds a little butt comfort without substantially raising my center of gravity. With the sides tucked under the thigh hooks and gunwales it stays in place. Also handy during lunch stops to pull it out to use as a seating pad.
It’s easy to adjust the placement for support and fit since it’s just a big raw piece of material. At times I have rolled the whole thing up and tucked it behind the small of my back to adjust my paddling position. I’ve never had it come out in a capsize or interfere with exits. I’ve considered cutting slits in it and running through a buckle strap or bungee to keep it in place but have never felt it needed such a modification.
Cool, I hope you can find a solution! A little off topic, but where do the thigh braces fall on your legs? Initially, mine were too far forward (I think), and they were covering a lot of my kneecap. Now, I moved them back, and they are more on my thigh. Not quite sure if that’s where they should be. The ones on my Tempest are lot better (IMO), larger with more padding.
One reason your legs can go numb is if the front edge of the seat is raised enough to affect circulation in your legs. A good test would be to cut a half inch piece of foam to sit higher up on, with the foam ending before the seat edge.
Closed Cell Foam and some experimentation is your friend.
I had similar issues when i first started doing longer trips and it took a fair bit of trial and error, a mash of advice and some painful days got to the bottom of it. The best advice i can offer is to try and see if a various combination of stuff works for you, your liable to find a solutions that is comprised of various changes that work for your body. For me it was a back rest change, and a seat upgrade (I was paddling the older NDK seat in my Greenlander Pro which is notoriously uncomfortable). Here are some things you can try:
Ditch the back band and use a block of micro cell foam thats a bit more vertical. This worked really well for me as I tend to have lower back issues from an old disk issue. The slightly more vertical and far more rigid support really helped to solve my back issues. The foam is soft enough i can still lay back and touch the back deck. it also fills the gap from the seat to where the back band started which keeps that pinch area gone.
Change the seat (or seat angle). The older seat in my boat was tilted a bit to far back which caused the front of it to press on my thighs and cut off some circulation (im pretty sure) which caused leg discomfort on long paddles. The newer seat is canted forward more and is a bit longer which really helped with the leg issues. You could accomplish something similar with thin foam adjustments on the base of the seat to re-shape it as needed. Again micro cell foam which can be sanded and shaped can really help here.
You could ditch the foot pegs for a foam block. On of my Greenlanders never had pegs and instead has two foam blocks for foot rests. It does not quite transfer power the way a solid peg does but its way more comfortable to press against than the metal pegs in my other boat. You can also angle the blocks, round them, shape them, and generally fit them as need be.
I personally dont like the full seat bottom pads (soft foam, stick on style) but I know many people find them quite comfortable. I tried one of those thing gel pads at one point with some success but never got it to stay in place right.
I use a 1/8 inch sheet of soft foam on the knee section to provide some cushion when bracing as well.
Other advice not outfitting related:
Stretching before helps a lot
Staying hydrated is important
Staying fed and energized on a long paddle is important. I keep some cliff bars in my life jacket at all times.
I was having hip problems a few years a go (increasing pain deep in the hip-joint with prolonged sitting in the cockpit that was only relieved by getting out to stretch.) Since then I looked up and regularly practice exercise routines that stretch and loosen up the piriformis muscles and those have proven very helpful in preventing that discomfort,