Hi katie.weisberg,
It may be worth considering a twin XL rather than a twin because the extra length may be helpful as your child grows older and bigger or if you ever use the mattress as a guest bed.
I’m not sure how you would define “healthy” but post #2 here and the more detailed posts and information it links to have more information about safe, natural, organic, “chemical free”, and “green” mattresses and mattress materials that can help you sort through some of the marketing information and terminology that you will encounter in the industry and can help you differentiate between them and answer “how safe is safe enough for me” so you can decide on the types of materials you are most comfortable with having in your child’s mattress. These types of issues are complex and are generally specific to each person and their individual sensitivities, circumstances, criteria, and lifestyle choices.
Once you have decided on which materials you are comfortable with having in your mattress then choosing a mattress that only contains those types of materials will be much simpler.
Post #2 here also includes links to the better forum posts and topics about mattresses and children that include more information and guidelines about buying a mattress for a child.
This is a “mostly latex” mattress (outside of the quilting materials in the cover) and as you mentioned has the advantage of being able to choose between two firmness levels so you could use the firmer side when they are younger and then switch to the softer side when they get older and start to develop more if they need some additional softness.
This is a latex/polyfoam hybrid that uses a polyfoam support core and a latex comfort layer. It has the option of being able to choose the firmness level of the latex comfort layer and to exchange the latex for a different firmness level if you need to but this wouldn’t be particularly important for a child. It is also very similar to the Ultimate Dreams Latex Hybrid here which is made by Dreamfoam (Brooklyn Bedding’s sister company) but doesn’t have the exchangeable layer and is a lower price which may also be worth considering.
There is more about a latex hybrid vs an all latex (or mostly latex) mattress in post #2 here.
As you mentioned this doesn’t contain any polyfoam at all and uses a wool quilted cover both as the fire barrier and also to help regulate temperature (wool is a great temperature regulator) but the wool is a more costly material than the polyfoam in the other mattresses you are considering. It also has the same benefit of having a softer and a firmer side like the Roma and is also a more “natural” option if that is an important part of your personal value equation.
Once you are down to finalists that are all choices between “good and good” and none of them have any weak links or lower quality materials in their design and if there are no clear winners between them then you are in the fortunate position that any of them would likely be a suitable choice and post #2 here can help you make a final choice based on your material preferences, your conversations with each of them, the prices, any additional extras that are part of each purchase, and on “informed best judgement” based on all the other objective, subjective, and intangible parts of your personal value equation that are most important to you.
Phoenix