We've just gone through the same process with my back. Took an eternity to get going in the morning, and only realised it was the bed when we went on holiday. Memory Foam was discounted quite early on. Not sure why but SWMBO has done a lot of reading up on it. We finished up in quite a good bed shop, and didn't look at the budget end. Sales girl was quite open about it, and would sell us one but was quite critical of the lower end products. "Remember you spend 30% of your time in your bed – get a good one".
We finished up with a Hypnos bed, Cost about £1200 for a Kingsize. But it's good. Instead of waking up at 3AM and lying there I now sleep right through and need the alarm to wake me.
Should get 10 years out of it, so works out quite cheap in the long run.
P.S. H M Queen sleeps on a Hypnos!!!