We moved 3 weeks ago and what was our master bedroom set is now our guest bedroom set. Didn’t realize what a headache mattress shopping, including in person tests and online reviews, would be. Thanks to MU and the forums we are going to give the Tuft & Needle a try. Because of the height of the headboard and foot-boards on our sleigh bed we definitely want a box spring and are finding it as much a headache (and in some cases as much an expense) as the mattress. If anyone has personal experience on a box spring that they like with their T&N mattress we would love to hear it!
Hi irishnips,
There is more information about the different types of support systems that are generally most suitable for different types of mattresses in post #1 here with a few examples of each of them. I would tend to avoid a box spring (that has springs inside it that flex) for a foam mattress and use either a foundation with a steel or wooden bedframe or a platform bed that can be used directly under the mattress.
A foam mattress will generally do best with a firm, flat, and evenly supportive support surface underneath it that has minimal to no flex under the mattress and for larger sizes with at least one center support beam that has good support to the floor to prevent any sagging in the middle of the mattress. The components need to be strong and durable enough to support the weight of the mattress and the people sleeping on it without some of the parts bending, sagging, or breaking over time. The support surface under the mattress should have enough surface area to prevent the foam in the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. If you are looking at foundations or platform beds with wooden slats I would suggest that the gaps between the slats are no more than about 5" (although less than 4" would be better and is what Tuft & Needle suggests in their Q&A page here). I would also be cautious about any parts, joints, or connections that may develop a tendency to start loosening and rubbing against each other and/or squeaking over time that can’t be located and easily tightened (this is a fairly common complaint with many lower cost foundations and/or wire grid platform/bedframes).
The general comments and suggestions in this topic would also apply to your mattress as well.
Most importantly … congratulations on your new mattress 
You certainly made a good quality/value choice and I hope you have the chance to share your comments and feedback when you receive it.
Phoenix
We used a Sleep Ez wood foundation. It was very easy to put together and is working fine.