I got mine through a sensory integration therapist - my mother knew her through her work and arranged for me to borrow one to try. The first one wasn't great and the second one I bought a few weeks ago.

The first one had "pockets" with Velcro, and a lot of "sandbags" to fill those pockets with. Only the packs or sand would move to the side of the pockets. To the lowest point, of course. Which meant on either side of me. So I don't recommend one like that.

This one is just stitched. It has pellets in it that make it washable. It's about the size of my bed, but I fold it over twice in the same direction until it's a "strip" the width of the bed. Then I put that part over my hips. I would always feel so vulnerable and naked at night, which is why I wanted to try a blanket. And it works!

Although putting it across my whole body just freaks me out. I prefer it just across my hips.

- I don't really care about the fabric as I use a duvet cover around it anyway
- Don't buy one like that first one I borrowed, as you'll end up between the weight instead of under it. Or you have 1 balled-up sand packet on your belly and nothing next to it; which just feels weird
- Beans and pellets are about equal in weight I'm told, but beans aren't washable.

Also, if you get one and find it doesn't work and actually makes you uncomfortable: you can also just put it over your legs. Or chest. Or, like me, hips. With or without folding it.

By the way there is both 'ball blankets' and 'weighted blankets'. They are often sold in the same webshops but are different. And sometimes they call ball blankets weighted, but they are lighter.
A ball blanket is basically filled with small balls; they offer different pressure. Calming sensation instead of calming weight. It's said to be especially effective for people who like or tend to 'roll' themselves in their blankets.

Mine is 22 lbs and it cost about $285 (converted from euros).

A lot of webshops offer the possibility of a trial by the way - hire it for 2 weeks and if it's not good, return, if it's good, buy (hiring cost is often a discount in those cases). Or a free trial where you only have to pay for shipping to and from.

The blanket doesn't actually help me sleep better but it at really makes me lie awake better. Usually a bad night would be crappy because I'd eventually thought of something crappy (trauma memories); I'd also get a neck-ache because of my tension even when not triggered or especially scared. That's lessened. And that makes a big difference.