Canoeing

We’ve hadn’t this mattress for 8 years now and we are in the market for a new mattress. Initially we had to modify our bed frame as it was slatted and the mattress sagged through the slats, all cured with a piece of plywood over the slats. However, fast forward to now and the mattress is canoeing. There’s a hump between us. We’ve routinely flipped the mattress and we weigh 125 and 160 lbs respectively so it’s not like we are heavy people. Also, we’ve had to add mattress pads since our sweat seeped through the sheets and stained the latex. Also, we are on our second cover since the first one shrunk when I washed it even though I did so exactly as they recommended.