We bought the Purple Mattress 4-inch straight from their website a few months ago. I absolutely love it. Unbelievable support. It uses a grid made from an elastic polymer to evenly distribute weight. Super supportive regardless of sleep position and the softest thing ever.
Definitely order the delivery option, it is crazy heavy. We splurged on the price because it will last years, and they have a pretty great satisfaction guarantee.
I will say it takes an adjustment period, I had terrible back pain and neck pain for a week while my spine was adjusting to a new surface and support. But after a week I slept like an angel. My favorite thing is coming home after a long day and sinking into it under my blankets.
I bought the "original" Purple mattress about a year ago and it has been the best decision of my life. I have a ton of sleep problems like back pain and sleep apnea and the Purple mattress has seriously helped me tackle all of these issues. The mattress was so easy to order and setup, I had it up and ready to sleep in less than an hour. It is firm (and has remained so) but not hard and has great support. The only downside is I moved once with this mattress and it is HEAVY. I mean it takes a team of men to try and move this bed and it needs a lot of hands to keep it under control. I know purple has "new" mattresses out but I live by the original I have now.
Price: $699+ for their original (firm) mattress, $1,299+ for their upgraded mattress (which lets you choose between firm, medium, and soft).
Sizes: Twin, Full, King, Queen, California King
Thickness: 9.5-13 inches, depending on which option you choose.