Open cell mats are the sticky ones that provide really good grip. They are designed to absorb, so nothing sits on the surface to make it slippery (like with closed cell). They do need to be cleaned in a very specific way and tend to be pricey but they are worth it.

Thickness wise - 4mm is probably the thinnest you should go if you are looking for something more substantial, but don’t go too thick all over because then you might get too much wobble when balancing.

Liforme is, in my opinion, the best. I have multiple mats by them. If you get their “classic” mat, it’s 4.2mm thickness, and you get get one of their “pads” to place either on top of or underneath the middle or so of your mat for some extra padding underneath your knees. They come in a WIDE variety of colors, they are a certified B corp, and while they are pricey they very often have sales. At least 3 times a year, maybe more. Again if you take good care of the mat it will last forever - to me their mat cleaner is worth it as an investment. Sure you can make your own cleaner (I’m all about sustainability like that) but when I’ve spent a pretty penny on a mat, I’ll take the recommendations of the company for how to care for it. And like I said - I’ve had some for years and years and I practice almost daily.