I bought SIMMONS, beauty rest, back care 3 at Sogo three years ago for about $6,xxx. (The price may be wrong.)
I like this one very much. And even I tried an other one at Sogo, which was about $1x,xxx. I like mine one much more cause it would not be too soft. At Sogo, you can really try to lay on each mattress. You know, different people would have different requirements.
I did not go to Megabox. I am living in HK Island. And 3 yrs ago, I just went to TaiKooShing Jusco and Sogo if I could find a suitable one. It seems that Sogo can offer more options.
And do you want a hard frame? It would be supplied by two different brand. If you need a mattress frame-- i.e. it looks like you are sleeping on two mattress with four reels at the lower mattress, you will have to face limited choices.
My mattress is a standard size of 4.5 ft wide. The hard frame of the bed is ordered at TaiKooShing Jusco.
Are you looking for some special size? If yes, it may need more time for delivery.