I sweat like crazy in some hot yoga classes, puddles, pools, lakes etc so I know what you mean. Did a crazy 4 hour Power Yoga class a few months ago with Brian Kest and a few people ended up in the sun simply in the studio and were in literal lakes on their mat.
For most people (aka people who don't end up in a lake) I think a mat like Lulu's The Mat which has an absorbent and really really sticky top layer is probably the best bet. This mat is really really sticky and will absorb quite a bit of sweat before it gets overwhelmed. Personally, this mat lasts me about half of a hot class before I just get too sweaty (they start to not work so well with age as well... so unfortunately even though it's an expensive mat they aren't something you'll keep around for years) and then although they are still pretty grippy I usually have to throw down a towel.
The natural rubber mats are awesome but same deal, since they don't absorb anything you can overwhelm them with sweat pretty quickly.
I never understood yoga towels but then I started a custom yoga towel company (yes, this is in a way a commercial post...) and had to figure out how exactly all of my friends used their towels without them slipping. Now that I've kind of got it dialed I find a blend of towel plus sticky mat is AWESOME!!!! I've got some notes below but also just look around in class at people who rock a yoga towel and see how they use it. I've seen one person (she was on the shorter side) who basically hacked down a mat by about 8" and then was able to tuck her towel under on both sides and ended up with a really awesome totally towel covered yoga mat and since the towel was tucked all over it never moved the entire class. Spraying the towels down before class helps a LOT as well.
-If you cover your entire mat with a towel and wet the towel down decently before you start you end up with a really nice grippy surface the entire class. It isn't as grippy as a dry mat but when you average out the grippiness over an entire class I think it's a better option than going without.
-I move my feet a lot in certain poses, roll over my toes and drag them a bit when performing certain moves and end up with a totally scrunched up towel down where my feet are in most of the poses. So what I do is that I tuck maybe 8" of the towel underneath the head of the matt. What this does is that by my hands where I tend to loose grip the fastest and also sweat the most I have tons of grip all the way through class. Down by my feet where I don't actually drop as much sweat as generally when I'm standing I'm at the center or front of the mat, I just have bare sticky mat so when I roll my toes over or something there is no towel to scrunch up. I REALLY like this solution.
My next plan is to try and integrate velcro into the bottom of one of my towels (seriously) and see if that helps if I also mate velcro to a mat:)
btw, I can't post my website url as I'm new but I have some really cool custom hot yoga towel designs:) custom yogi towls dot com