Redmage has singled out the best rope work ideas that solve the issue that you are having.The images he sent you to are a solid start point. Let me add some words to show why it's done as shown.
The problem of pressure points comes from the ties directly tightning down on the wrists or legs. The solution is to not tie directly about them. You will tighten the bounds indirectly.
Take your length of rope (and make sure it's good and long) and double it over on itself to make a double rope with a 'U' at one end, and two loose ends at the other. Then lay it across the limbs you plan to bind, such that equal amounts are on each side of the pair of limbs. The reason we folded the rope over is that two lengths of rope form a wider surface then one. By doing that we mitigate the dig into the skin if we'd gone with just a single cord. More surface area = less pressure on the bound persons limbs.
Now taking one end of the doubled rope, start to make a figure eight pattern about the limbs. Repeat with the other end weaving in and out. You'll be creating a figure eight pattern. You are building cuffs this way.
Eventully you'll end up with both limbs having snug cuffs of rope about them, and a thick band of rope between the limbs you are joining. Now you take your remaining ends of rope, and loop about that center band. Here is when you go for tight. By cinching down on that band you will tighten the ropes about the limbs to a nice snugness. But as the pressure is not direct, the bond can stay on for longer. The rope takes all the tightning pressure, not the limbs.
Once you have that center band looped to your liking, use the two loose ends of the rope and the loop to tie it off so it stays tight.
And there you have it, a comfortable, longer time bondage.
It takes a bit of practice to get them to work well, and at first you will spend a lot of time doing the tie. But with practice it becomes second nature and you'll get frightingly quick. You'll get the idea as you do. Like sex you can see pictures of it a dozen times and understand, but until you get hands on practice you don't 'get' it.
Good luck! It's clear that you are paying solid attention to your partners state, and that's the key thing for such play. I think you'll do well.
Myriads