In 2017 I ordered from Seattle Mattress Company (SMC) this custom sized 7-in thick 6-ft long "SMC Marine Highlands Twin Mattress made with 100% Natural Talalay Latex" for $1325 to fit the size and outboard contour and angles for our cabin's amidships starboard settee/berth in our 34' LOA wooden carvel-planked double-ender sailboat. SMC also custom made for us a fitted sheet (beige) and fitted mattress protector. For mattress ventilation and added comfort I purchased a very effective Froli support system (see NickleAtlantic.com). Also included is the contoured epoxy-coated 3/8” marine plywood lifting board that I made. The new cost of all these items in 2017 was about $1800.
Soon after installation I slept on the mattress two nights and had one afternoon nap, and I found it as comfortable as any high quality mattress system I had previously experienced. However, after that initial trial, the mattress has never been slept on or even napped on again. A small 30 y/o wood boat, at least in my hands, was an ongoing source of compelling projects, despite its limited interior space. Our port berth remained a hard mahogany surface and was soon covered with tool chests, vacuum system, and shelves. The starboard berth with its fancy new mattress system was covered with several sturdy waterproof bed pads and served as a desk surface and storage space for light weight project parts. So the boat became a mini-workshop and never left the dock. Recently our long-planned haul-out for a truck and crane trip to our home patio for a big fix-up was cancelled when serious wood rot was discovered in the boat's spine, leaving boat disposal as the only sensible and affordable option. So the boat is now history, and its nice gear is being sold locally via Craigslist.
Basically this mattress is a high quality custom boat mattress sized for very comfortable sleeping for one person. It of course features a gently curved and beveled outboard side, with all the other mattress angles very close to 90º. Even though the boat for which it was customized was small, the berth was in the middle of the fore and aft length, reducing the amount of outboard width tapering. It now seems likely that this expensive and barely used mattress system could fit reasonably well in other starboard berth spaces of similar size (see the final photo for detailed dimensions and angles).
For access to spaces underneath the berth the plywood lifting board has proved to be invaluable for angling upward the inboard side of the mattress and Froli support system as one stable unit. I simply used a stainless eye secured near the middle of the inboard edge of the lifting board at a point lining up overhead with a a laminated cabin top frame where a matching eye was securely mounted. The mattress system is a bit heavy, but a 1/8" parachute cord with a bowline in one end looped through both eyes with the distal end looping back through the bowline provided a 2:1 lift, aided of course by my other arm after the lift was started. This was then secured with a trucker's hitch, providing a simple and very effective system. For prolonged work underneath, a couple of cut-to-fit small boards were used to prop up both ends of the angled plywood lifting board to take most of the load off the lifting eyes and ceiling frame.
Also included: four extra light blue Froli grid tops; four extra grid bottom pieces with one side prong on each cut off to allow use along an edge. Note that all the Froli components are available either a la carte or in kits on the website at reasonably prices.