Hi KevinTMC,
There is more about the three most important parts of the “value” of a mattress purchase in post #13 here.
The first part is comfort and PPP (Posture and alignment, Pressure relief, and Personal preferences) and this is all about how well you will sleep on a mattress. This is the part where the Tuft & Needle could certainly be a suitable choice for higher weights because it’s in a firmer range and because of the design of the mattress you certainly wouldn’t be bottoming out on the mattress so it would “hold” your weight. This is where the trial period and return policy would be important so you can assess whether the mattress is suitable for you based on your actual sleeping experience.
The second is durability and the useful life of a mattress and this is all about the durability of the materials inside a mattress and how long you will sleep well before foam softening leads to crossing the thresholds between sleeping well on a mattress to sleeping OK to tolerating a mattress to finally deciding to replace it. With lower density materials you would cross these thresholds faster than you would with higher density materials.
Mattress warranties only cover defects in the materials and they don’t cover the gradual (or more rapid in the case of lower quality comfort layers) loss of comfort and support that comes from foam softening that is the main reason that most people will need to replace their mattress. In other words warranties have little to do with the durability or useful life of a mattress or how long it will be before you need to buy a new mattress. If there is an actual defect in the material it will usually show up early in the life of the mattress. There is also more about mattress warranties in post #174 here and there is more about the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here.
Knowing the quality/density and durability of the materials in a mattress is a much more reliable way to assess the durability and useful life of a mattress than the length of a warranty.
You can also see some comments about the Tuft and Needle (and some of the other “one choice fits all” mattresses) relative to higher weight ranges in post #3 here that would apply here as well.
While there is no way to quantify how long any mattress will last for any particular person, if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new and meets the minimum quality specs that are suggested in the guidelines here for your weight range then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with a slightly lower density support core relative to your higher weight it would probably still be close to this range even though it may be a little less so it would be prudent to reduce your expectations slightly and if the mattress lasts you longer than this I would consider it to be “bonus time”.
Having said all that … the Tuft & Needle is also in a lower budget range where there are always some tradeoffs involved and while the base foam is a little lower density than I would normally suggest in your weight range … it’s not far off the minimum guidelines and it would certainly be a more durable choice than most other mattresses in its budget range. Since “value” is always relative to how a mattress compares to any other “finalists” you are considering … I would still consider the Tuft & Needle to be a good quality/value choice compared to most other mattresses in its budget range and to find a mattress that is more durable you may need to increase your budget.
There is more about the different types of support systems that would normally be suitable for different types of mattresses in post #1 here.
There is more about the different types of mattress protectors and the pros and cons of each of them in post #89 here.
Post #7 and the other topics it links to should be helpful with choosing sheets.
The pillow topic here and the other topics it links to should be helpful with choosing a pillow.
Hope this all helps 
Phoenix