I've been using saunas for 10 years or so, and have been in hundreds of different ones over time as I have had to seek them out while traveling.
Honestly this cheap one really works for detoxing:
ebay.to/1QTcW7aI've tried other FIR saunas (portable and wood) and sometimes they don't get hot enough to make me sweat a decent amount. That particular model gets nice and hot really quickly, and I actually set it one level below the hottest. Normally with infrared saunas I put them on the max temp and am sad when they aren't hot enough. The plastic smell goes away after the first use and I doubt it would be a major issue, especially since your head is not inside.
It's far from the finest sauna experience in the world, but it actually gets the toxins out quite well.