When it comes to sleep there are few things more important than your mattress. For most people, finding a mattress is a nightmare, and there aren't very many resources that will tell you honestly where to find the best mattress.
The problem is that people are different. The experts don't have an answer for the "What is the best mattress?" question because there is no mattress that is going to be the best for everyone. We are going to focus on the mattress that is the best for 90% of people.
Forget coil count and thread count. The most important factor when buying a mattress is firmness. Most people are most comfortable sleeping on a firm mattress. You want to find a mattress that is able to distribute your body weight, but is also comfortable to fall asleep on. If your mattress is too soft, you may wake up sore, because your shoulders or hips are sagging.
When it comes to the type of mattress, most people are still prefer a traditional spring mattress. The newer all foam mattresses simply do not offer the firmness and support that most people prefer. Having a pillow top or foam top is generally good as it allows you to be comfortable on a firmer mattress.
When it comes to numbers the more coils the more evenly the mattress support, and the more thread the softer the mattress material. Not all coils are created equally. Also make sure to check the raw amount of steel the mattress uses. A million tiny coils will not offer the support you need.
There are a lot of great mattresses out there. The landscape is constantly changing. To get the best bang for your buck try ordering through a online store which offers relatively few choices. These stores have the lowest overhead and more of your money will go to the actual mattress quality than anywhere else. If you live in the northeast, your best best is Saatva. If you live anywhere else it is hard to say. Maybe ask saatva to come to you.