Hi BrissieMum,
Not at all … and as a matter of fact I’m grateful. Hopefully your experience will help many others.
Bamboo has a very soft and smooth “hand” and it’s very common to find it blended with polyester (as well as other fibers such as cotton). Temperature regulation is controlled by many factors (see post #2 here) and by itself this probably wouldn’t be enough for me to exclude a mattress or be concerned for its sleeping temperature. It could still be a stretch knit (polyester or other fibers can be part of a woven or a knitted fabric).
This could be a very comfortable combination for many people. This would be similar to the 6" plus 2" construction which is quite popular here … especially with a slightly softer core (with a firmer core many people may need a thicker topper).
I think Latex Gold makes high quality Dunlop latex and don’t use any SBR. I don’t know the specific certifications that they have but I don’t think they would have any difficulty passing any of them.
Their site says this would be in the 12 - 15 ILD range and the density would seem to confirm this. If you are testing a mattress locally though I wouldn’t pay much attention to ILD and would let your body tell you how well the mattress worked in terms of PPP. ILD can be a little misleading with Dunlop because it also has a higher compression modulus so it will feel firmer with deeper compression than the equivalent ILD in Talalay. It is also denser than very soft Talalay in a similar ILD. “Too soft” or “too firm” is always relative to the individual person and I would let your testing answer this.
I don’t know the prices you are looking at but it seems to me you do have a “legitimate contender” 
Phoenix