A few years back, I posted a modification idea about using the colorful kids swimming noodles as backrests. They simply slide over the cockpit cables and are great a accessory for the boat. I was bombarded by replies saying that the sun would destroy them in no time and they would fall apart, etc. Folks- the only reason I just changed mine- after 2 years- is because there is now a thicker version at the box stores. The sun did not make a dent in the noodle after 2 years. This is a great, simple modification that your back will thank you for.
any negative comments on the use of pool noodles for lifeline mounted back rests must have been on another site or your local sailing crowd, that didn't happen here. It is a great idea. A number of folks use them here. I do. I chose to cover mine with Sunbrella, mostly for looks to match the other covers on my boat. I also chose to put PVC in the core so the lifeline wire, pelican hook and stop would not abrade the noodle. I have found that they tend to shrink over time and on my 23 the lifeline is long enough that it takes more than one per side actually about one and two thirds. I tape them together before I slide them in the cover. When they shrink I change them, about every three years or so. You're right, your back will thank you.
Mine a touch more than $3 each but I had most of the materials already.