What Play Yard is the best for a toddler?

I have a regular pack N Play. No bells or whistles... And I loved this for my newborn/infant but now that she is almost 1 year, the little mattress is very flimsy. I need a Play Yard or Pack N Play that is sturdy for my little one to play and sleep in without the mattress sagging almost on to the support bars underneath. My daughter will be sleeping in one for up to 7 months and I want her to be safe and comfy. Are all Play Yards like this? Or do you know of one that fits my needs?