I think the best thing to do is put the mattress outside in a dry place for a week or so if you can (this is assuming the mattress is new and will be offgassing a lot at first). When DH and I got our mattress (before I realized I could get an organic cotton/latex/wool one for about the same price

: ) we put it in our room, opened the windows and closed the door then slept on our futon in another room for a week. By then it didn't smell strong at least.
I think wool toppers are wonderful, but they are very breathable (which is generally a great thing!) so I don't think they would prevent you from smelling/breathing fumes.
For the record, my DD's mattress is organic latex/cotton/wool and didn't smell bad at all! It is so nice, I wish we had gotten one!