My husband and I had the same problem with a mattress 3 years ago that wasn't more than 2 or 3 years old. Sinking in the middle. He weighs about the same as you and I am just over 110. When we went to the mattress outlet they told us that full beds and queens don't offer a lot of support in the middle. King size beds have two twin size boxsprings so the support in the middle of the bed is great from the two boxsprings meeting together. We were already looking for a king anyway so we got one.

We got the Serta perfect sleeper though. ITs awesome, we have had it 3 years now and there's no sinking in the middle. I love it. So if you can I would look into getting a king size. And a little hint, Tax return season is just around the corner, if you wait about a month the mattress places all have huge sales cause everyone getting their returns thats how we got such an awesome deal on ours.