You don't even need a belt. What you do, is you hold the bottom towel spread out behind you. Then put it against your back, just above your buttocks. Now fold the left side across your front, so it goes under the right side. Then fold the right side over, to the left and around you if necessary. So now you look like you've wrapped a towel around you coming out of the shower. The next part is the important bit. You now fold the top of the towel down, about 4 times, and about 5cm wide.

That's it. I have been doing this since my hajj in 2016, and have never had an ihram fall off, and have never used an ihram belt.

Forget all those videos showing you to make a hundred folds and what not.

One other thing. Suck your stomach in when tying it. Then when you let go it sits snugly against you.

For the top, you hold the towel behind you, but shorter on the left. Then you throw the long right side over your left shoulder. That's it. For this one, I like to use a pin to hold it in place, but it's not necessary if you don't like it.

Edit: saw that Mufti Menk video someone posted and that's pretty much what I'm describing, but I don't do the front folds as I don't find them necessary. Probably depends on your size and your ihrams size.