I don't know about you, but my ability to sleep on the ground ended around age 15.

27 oz is a heck of a heavy pad when you consider options like CCF foam and NeoAir. But you have to decide - the considerations are always budget, weight, and comfort. Which is most important?

For me, comfort and weight came first and equally - I have a NeoAir medium, weighs 13 oz. Budget was important too - but as with a good sleeping bag/quilt, I also consider how many of the item I'm going to try and find wanting - the regular self inflating pads are all the same to me, uncomfortable, leading to tossing and turning and no sleep at all, and getting up in the morning with sore joints and hips. So I spent the money, and found that it was well spent on the NeoAir - I typically get an hour or two of sleep at a stretch, waking to turn over, sleeping another hour or two... vast improvement over no sleep.

Yes, you do need something, especially if the temps are expected to be below freezing. A CCF pad will be the lightest and cheapest but provides the least padding. If I could get away with that it's what I would have. Alas, I require actual sound sleep to backpack and be sane/pleasant to companions. So when I can't have my hammock, I take the NeoAir.

If I were winter camping, I'd get a short Exped Downmat. For someone of my stature it would be adequate and weigh about the same as your REI pad, only work for a much lower temperature.