>>11342932
A few kneeling tips, I suppose:

For nadu/seiza, do keep the top of your foot flat on the floor. This is very very important. Not everyone can do this right out of the gate, it may take some stretching to achieve. The nadu picture is unrealistic in that I've never seen anyone capable of doing this with shoes. Keeping the top of your foot flat to the floor is the most important part.

If you sit on the ball of your foot instead of the top of your foot, your knees will start to hurt pretty quickly. You want to distribute the weight over your whole shin, but if you're sitting up straight it should mostly be on the ankles. It isn't the knees that should be in pain, but the ankles.

Find the right position for your feet. For me, the only comfortable position was to cross my feet, holding the arch of my right foot in the instep of my left foot. For nadu I'm able to open my legs while keeping my feet in this configuration. I also switch which foot is on top sometimes.

As for what's easiest to kneel on, the answer turns out to be that padding under your feet sucks. It's harder to sit seiza on a soft bed than a hard floor, because the padding bends your feet backwards. A seat cushion, with your feet hanging off, lets your feet bend forwards a little, making it easier because your ankle has to stretch a shorter distance.

You can also do picrel, taking the weight off your ankles by shifting it onto your hands. It's another good worship/submission pose too. Really useful for training nadu/seiza.

Don't feel bad about doing this. Not a lot of people can sit seiza properly first try without injuring themselves. I recommended using both techniques.

It gets easier. Consistent practice and stretching is better than blowing out your ankles and injuring yourself. Don't injure yourself. Don't kneel for hours overcoming the pain with willpower until your legs go completely dead and you have to flop and crawl into a recovery position like I used to.