We are upgrading to a King from a Queen.  We currently have a Simmons beauty rest that is about 10 years old.

I am a big guy 6' 4" 215 lbs and have an achy back.  I always thought I should have a firm mattress, but after going and laying around on some, i found I really like something a little softer.  I like some of the temperpedic beds also.

So, I see costco sells some memory foam mattress that get mixed reviews.  I am half temped to try one out and if I dont like it, take it back.  However, none of them come with a foundation.  Should i just find a cheap box spring around town or should i get a specific foundation?  

Any suggestions on what to do about a foundation would be great.

Depending on the reason behind the move up, going to a king is great. However, you have to remember the cost of bedding as well as the increase in the cost for the mattress can be an eye opener. My wife and I have been sleeping in a king for over 30 years. I tend to flop around at night and we have fewer collisions on a bigger bed.

I'm not a memory foam aficionado as I'm too hot of a night sleeper. Memory foam is hot to me. Most of the memory foam beds we tried were too soft. So I would go the DIY latex option. There are a plethora of them mentioned on this forum.

You may want to see if there are any latex mattress companies in your area so as to try out a mattress before making your buying decision. Mattress shopping can be very trying for most folks. There are a lot of snake oil salespersons out there. So be aware.

Foundations, should you purchase a mattress from one of the folks recommended from the forum you should ask their opinion. We are using the platform from our old water bead as the foundation. You could set a car on top of it and not budge it or cause any damage.

Hope this helps ....