The smell will completely dissipate in a short time. We've used a foam topper for years and it's the most comfortable bed I've ever had. I don't know much about the toxicity, but I can't imagine it's much worse than whatever they make regular mattresses out of.
An added benefit though is they are by their nature "allergy free" (as long as you aren't allergic to the foam, that is).
They don't harbor dust mites which cause allergies for a lot of people.
They do retain a bit more body heat than other types of mattresses so you may need to keep the bedroom cooler.
"I did it for money and for a woman. I didn't get the money, and I didn't get the woman"