Hi Miko,
I’m not sure why breathability would be an issue (wool is very breathable) but my bigger concerns would be trying a combination I wasn’t familiar with in terms of comfort (wool over polyfoam could become quite firm depending on the firmness of the polyfoam and the specifics of the topper) and on the topper “flopping around” as the bed was raised and lowered and possibly becoming damaged in the mechanism or shifting the wool over time. If I had a murphy bed (see post #64 here) I would probably tend towards a “finished mattress” that I had tested with a stiff base layer that would stand up to longer periods of time on edge where the risk of shifting or sagging layers was minimized and the manufacturer confirmed that it would work well inside the murphy bed.
The ideal would be that the murphy bed was suitable for supporting a mattress by itself without a foundation at all but if it isn’t (I can’t see the details of the support surface on your murphy bed) then you would need a foundation as well. If you do need a foundation I would tend to use a low profile foundation because you are limited to 11" in height and you won’t need a foundation with the narrower gaps that would be necessary for a mattress with a latex base. A base with flexible slats or tension adjustable slats (like the Laxeby) could either help or detract from the feel and performance of your mattress depending on the thickness of the mattress and on the specifics of the combination. Your highest odds are to test a mattress that works well on a firm non flexing foundation and then to use something similar under the mattress (either the murphy bed itself or a foundation if it needs one) so you don’t have another variable to try and “match” the characteristics of a flexible base that you haven’t tested in combination with the mattress.
BE is Berkeley Ergonomics and at this point they don’t have any retailers in Canada. NOTE ADDED: they are now available at Calgary, Edmonton & Sherwood Park Mattress Stores | Mattress & Sleep Co. who are one of the members of this site and will ship across the country.
Overall I would tend to focus on a mattress that I was familiar with the combination of materials (through personal testing or at least using similar material combinations to those I had tested) and didn’t have a tendency to shift or sag.
Phoenix