I was in the trade for many years. Some basic rules for buying a bed.
1. Buy the best you can afford. Ideally that should mean a good quality mattress on the manufacturer's own matching base.
2. If you do buy a wooded framed base (with slats) and you also buy any sort of sprung mattress, be sure to cover the slats with a piece of firm hardboard, the same size as the mattress.
3. Do not be tempted to save money by putting a new mattress on an old base. The old base will transmit its earlier years of wear onto the new mattress and correspondingly reduce its life.
4. Ignore claims of reduced prices. The bedding trade is a racket and almost all prices are suspect. Places to avoid are the big high street or business park companies. Usually a decent quality private store will probably offer the best and most honest advice.
5. Don't be afraid to lie down and move around on the bed that interests you … and if that means ten or fifteen minutes, so be it.
Sleep well.