Hi SleepNYC,
While all soft foam materials will soften and impress to some degree over time … higher quality/density materials will do so less and over a longer period of time than lower quality/density materials. The polyfoam layers in the Tuft & Needle mattress are @ 2 lb density which is a good quality and durable grade of polyfoam and would generally be suitable for your weight. You can read more about the quality specs of different types of foam in post #4 here.
Phoenix