I am currently sleeping on an old, too old, latex foam mattress.  While still comfortable its on its last legs, the cover has worn through top and bottom and its started to shed bits of foam.  I am considering replacing it with a mattress from Costco, an Ara twin.  The mattress only as the foundation still seem usable.  Is there a consensus on the quality of this mattress?

I doubt many here know of that mattress, just to warn you.
I say that with CostCo, though, if they allow a return on it within however many days if you don't like it, then go for it.