origins pocket 1500 or 2000?

Hi,
I weigh 16.5 stone, and my wife about 12-13, and we're looking to buy a new double mattress.
I think I'd prefer something quite firm. As a student, I used to sleep on a futon, which felt great for my back.
The Origins Pocket 1500 seems to fit our budget. Would we be better going for the 2000 spring version?
Our current bed has sprung slats, but we're planning to replace that too. For aesthetic reasons, we'd like to go for a wooden bed frame. Is there anything we should look out for? Are there any brands/shops to go for or avoid?
Thanks