Hi creativepart,
This foundation post here (and the two other posts it links to in the second paragraph) has much more information about box springs and foundations and which ones would generally be suitable for different types of mattresses.
Whether or not you could keep your current foundation/box spring would depend on what type it was and whether it was suitable for the type of mattress that you purchase and on its condition (no sagging or soft spots and still in new condition) but if it’s 8 years old I would tend to replace it.
Phoenix