Hi McJenn,
This is a preference choice so only you can decide which type of mattress you tend to prefer but there is more about innerspring hybrid mattresses vs all latex mattresses in post #13 here and the posts it links to. I would keep in mind that every category of mattress includes hundreds of individual mattresses that are very different from each other and some of them may be a great match for you in terms of PPP and others may be completely unsuitable for you to sleep on because they have a very different design even though they are in the same general category.
There is more about the different ways to choose a mattress (either locally or online) that can help you identify and minimize the risks involved in each of them and there is also more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you make more meaningful comparisons between mattresses.
Unfortunately I can’t feel what you feel and there are too many unknowns, variables, and personal preferences involved in choosing a mattress for anyone to know which mattress would be the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) based on specs (either yours of a mattress) or "theory at a distance (see mattress firmness/comfort levels in post #2 here) and I also don’t know which of the mattresses you listed are the best match for all the parts of your personal value equation that are most important to you but I can certainly speak to the quality of the materials in all of them.
You have done a great job choosing high quality mattresses as your finalists and none of them contain any lower quality materials or weak links in their design so I would focus more on which of them is most likely to be the best match in terms of PPP and on which of them meet all the other “value” criteria that are most important to you since durability isn’t likely to be an issue with any of them…
When you are down to finalists that are all choices between “good and good” and 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 local testing, your conversations with each of them, your confidence about the suitability of each one, the prices, the options you have after a 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.
Post #2 here includes a number of links to some of the better forum posts and topics about mattresses and children which include some guidelines for children and more information about many of the better options I’m aware of as well. All of the Childrens mattresses you mentioned would certainly make suitable choices although you won’t really need more than about 6" of latex for younger children. The Morgongava is flippable.
While there is no way to quantify how long any mattress will last for any particular person (or child) … if a mattress is well inside the comfort/support range that is suitable for someone and isn’t close to the edge of the range that is too soft when it is new (see post #2 here) and meets the minimum quality specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with higher quality and more durable materials like latex or higher density memory foam or polyfoam (in the comfort layers especially) it would likely be in the higher end of the range or even longer.
It’s always more realistic to think of 10 years as a maximum reasonable expectation for any mattress no matter what the quality of the materials and then treat any additional time after that as “bonus time” because after about 10 years the limiting factor in the useful life of a mattress will often be the changing needs and preferences of the person sleeping on the mattress and even if a mattress is still in good condition after a decade … a mattress that was suitable for someone 10 years earlier may not be the best “match” any longer. With higher quality materials throughout a mattress and/or for people whose needs and preferences or physical condition or body type hasn’t changed much over 10 years then “bonus time” or even “extended bonus time” with higher quality/density materials like latex is much more likely than with materials that are in a lower quality/density range.
If you purchase a firmer mattress and your sons just need additional softness or thickness (depending on how they develop as they get older) then if the mattress is in good condition (which it would be if you use high quality materials) it’s a simple matter to add a topper to extend its useful life.
In the same way if you have a component latex mattress you can also rearrange the layers to firm up the support if necessary and then add a topper if they need some additional thickness or softness on the sleeping surface as well.
Phoenix