Mattress Upgrade?

I've been a tent/hammock camper for years. Having a mattress in my TT is awesome BUT this mattress that my camper came with is horribly firm. In a thought to upgrade I'm looking at Memory Foam Mattresses since they are cheaper than a regular mattress and I feel they would be more comfortable also.

I'm also drawn towards some weight savings though...and am thinking about getting a pair of Thermarest Dreamtime air mattresses instead. I've never slept on a Dreamtime but all the reviews are great.

Has anyone else gone this route to save some weight? Does that mattress compare to a 8 inch memory foam?