Origins Pocket 1500 mattress on an old Ikea sprung base?

Hi, I currently have a silent night 1400 pocket sprung which I used to find hard until I replaced a slatted bed with this Ikea sprung base in order to soften it up a little. However, it has now sagged! I am not sure if that is because it is 4 years old or because the base has not got enough support. Either way, I need a new mattress.
I think I have decided upon the Origins Pocket 1500 mattress medium as a replacement and I am happy to invest in a base to make it last and provide the correct support. I think a medium mattress on a sprung base may be too soft and cause the mattress to sag earlier than a harder base. I do turn a lot and sleep on my side and back. I am 11.5 to 12 stone. Your experienced advice would be appreciated before I order.
Many thanks
Chris