Hi coolmonk,
I’m not sure you will need a topper at all for this mattress for a 5 year old and the only real reason to add one would be if for some reason the mattress wasn’t suitable by itself and you needed to make it softer.
If you did decide to add a topper (and I would order just the mattress first so that any topper choice was based on actual experience) then wool (or any natural fiber) would be more breathable and temperature regulating than any foam including latex. Even though latex is the most breathable category of foam … all foam is more of an insulator and less breathable than wool
You’re right it really is a matter of preference so while I can’t tell you what to choose or which may be “better” for you (that’s a matter of your own “personal value equation” and preferences) … I can certainly share some thoughts about the pros and cons of each that may help you decide.
Both are great value but if budget is your primary consideration then of course the Pure Eco is the most economical choice.
If temperature regulation is a primary consideration then natural fibers (especially wool) are more breathable and temperature regulating than any foam including latex and while the 7" natural latex has some wool in the cover … it wouldn’t be as breathable as the Pure Eco (but it also wouldn’t sleep “hot” either because it does have some wool and latex is a more breathable foam).
If you like to snuggle with your kids on their mattress … then latex would probably be more comfortable for you than a natural fiber/innerspring because of the response and natural resilience of latex.
In terms of durability then latex would likely have the edge over a fiber/innerspring mattress.
If flexibility of design and some of your longer term options are a primary consideration … then the 7" natural latex would probably be a more flexible choice because you could add an extra softer layer as part of a 3x3 latex design and put it inside a new cover and “re-use” the latex layers. You also have more options for re-arranging the layers if needs or preferences change than with the Pure Eco. Of course both would have the option of adding a topper if it becomes necessary to add a softer comfort layer when they get older.
If you did decide to add a latex topper to either one (which really isn’t necessary with either at leas for now) … then you would lose the benefit of sleeping directly on the wool with either mattress unless you also added a wool topper as well.
If you did decide to add a wool topper then it may be worth considering the lower cost of the 6" SleepEz special here which has a stretch knit cover without any wool quilting and then add the wool topper on top of this.
Hopefully this can help you identify the pros and cons which are most important to you and make the final choice that is the best “fit” for your needs and preferences. They are both great options IMO.
Phoenix