Hi 901-Memphis,
Based on “averages” … a medium firmness range will generally be inside the largest percentage of the bell curve that would be suitable for most people and with your weight range a softer choice could be more risky but of course not everyone fits inside the “averages” that would work well for most people which is the reason that a good trial period can be an important part of the “value” of an online purchase.
The break in and adjustment period will vary with different people and different mattresses (higher quality and more durable materials can take longer to break in) and it can also depend on what you are used to sleeping on but for most people it would be somewhere in the range of about a month or less although for some it will be much shorter (some people sleep well on a new mattress right away or after just a few days) and for others it can sometimes take several months.
Are you experiencing any actual “symptoms” when you sleep on your mattress or is it just a matter of preferences and more subjective “comfort” issues?
[quote]We will definitely now be making a size change, and going to a king size bed. Do you have any insight on this Zinus frame/foundation?
www.amazon.com/gp/aw/d/B00W4DCK18/[/quote]
Any mattress with a polyfoam support core 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 (bedframe and foundation or platform bed) 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, shifting, or breaking with extended use. The support surface under the mattress (which may be slats or a steel or wire grid) should have enough surface area to prevent the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. If a foundation has a slatted surface then I would suggest that the gaps between any slats are no more than about 5" (with 1 x 3 slats) although less than 4" would be better yet.
I don’t have any specific knowledge about or personal experience with the Zinus platform bedframe so I can’t speak to how strong it is. The slats appear to be 3" apart (according to the questions and answers) but I would make sure that the slats are rigid and won’t easily bend or break under your weights and the weight of the mattress (many lower cost bedframes and foundations use slats that are thinner or use lower quality and weaker wood which can bend or break too easily).
There is more information about support systems (bedframes and foundations or platform beds) that are generally suitable for different types of mattresses and some examples of each of them in post #1 here and some of the information and comments in this topic (which would apply to any foam mattress) may be helpful as well.
Phoenix