Our V-berth mattress on our R27 (2013) took an instant dislike to us (and we to it). So before even giving it a second night, we contacted a local mattress maker and replaced the factory foam with latex. He pulled the cover off, detached old foam (it is glued to the back boards), put on new foam, and recovered with same factory cloth. That part worked great.
The new foam was a big improvement, and for those who are reasonably comfortable on the stock mattress, replacing it with 4 inch memory or latex foam might be all you would ever want or need. For us, the factory foam was intolerable. The new foam improved it to the tolerable level, but it still leaves some to be desired.
So we think we will add a topper of some kind. Maybe not until spring. We are thinking a 2" topper might do it. But 3" for sure will. Our home mattress is 10" thick high quality memory foam. Not realistic to expect 4" of any kind or quality of foam to offer that level of comfort.
The latex base, coupled with a good topper, may come close enough. But it will nullify the convenience of the modular mattress pieces if we do a single piece topper, as opposed to making it somehow modular as well. I keep pondering possible ways to do that, but the only good one (having a custom set done by a mattress company) is out of the budget for now.
My understanding is that the R29 & R31 are different set ups mattress wise. Better and thicker foam from the get-go. The issues are greater for us with the shorter tugs. Postings on the forum about the mattress shortcomings are many, and we built our tug knowing we would have to address it post delivery (the factory gave us a flat no on any kind if upgrade)..It is one of the few things (heck, maybe the only thing) where I think the factory has not really addressed actual use and function. Addressing it post delivery can prove very expensive, much more than an upgrade option through the factory would likely need to be, if they were willing to do it.
Still, we love our tug, of course. And our use right now doesn't call for a lot of overnights. So we can easily deal more with it down the road (or waterway).
Gini