Hi nfries88,
I would also make sure you are confident that a mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) as well unless of course you are one of the fortunate few that can sleep on anything.
Both of these are good quality/value choices but Tuft and Needle is a polyfoam mattress and the Monaco is a memory foam mattress so they are very different from each other and use different materials. Polyfoam is a lower cost material than either memory foam or latex but is also very different in terms of how it feels and performs. I would make sure you talk with them so you have some confidence that either mattress would be suitable for you (they are both firm mattresses). The Tuft & Needle has a refund policy if their mattress doesn’t work for you but the Monaco can’t be returned or refunded.
The first place I would start your research is the tutorial post here which has all basic information, steps, and guidelines you will need to make the best possible choices but the first step would probably be to decide whether you prefer a polyfoam mattress or a memory foam mattress (which uses memory foam in the top layers of the mattress).
The tutorial post has a link to a list of some of the better online memory foam options I’m aware of and if you are in a budget range of about $500 or less for a queen then Restava, Dreamfoam, and My Luxury Mattress would have options in that budget range.
There is also a list in the Tutorial post to the members here that sell online and If you are looking for a polyfoam mattress then Tuft and Needle5" or 10" and the Dreamfoam 12 in 1 customizable mattress (which can be customized in different ways) would both be in your budget range.
Phoenix