Looks like a good choice! I like the quality of their mattresses, so I bought mine there also. Ikea didn't have that 48" wide mattress when I shopped for one, so I bought the Sultan Florvag twin (since replaced by the Malm), which measures 38.25"w x 74.375"l x 3.875" thick. Initially, I designed my trailer to carry cargo to camp, and would fold the mattress back and strap it down with bungy cords to make room to put the large cooler and water carriers inside (strapped to the e-track on the front wall).
waterproof carpet, e-track on front wall
mattress folded, strapped down
hold-down loops flanking mattress
cooler, water secured to e-track
head area (towards trailer rear), body pillow shown
foot area (at trailer nose), e-track patially covered by comforter
My reason for doing that was to use the weight as a counter-balance for the heavy loads in my rear galley/storage area. I also utilized the free-space on either side of the mattress to mount hold-down loops.
copied from a prior thread>>>> working on it wrote:My trailer is a 4x8 also. I didn't want to spend the extra money to have a custom 46.5" wide foam mattress made, so I got a 3" thick Twin foam from Ikea. I chose a foam mattress, for the insulation from a cold floor, the ease of folding it over (when travelling, I use the front half of the cabin as a cargo bay), and a spring mattress would not be able to fold nor fit thru the doors! And, I personally like a firm bed, and 3"+ of foam over plywood will be firm. To fill in the gap to the wall, I bought a body pillow at Walmart. At 54" long, it'll support a sleeper for the majority of his/her length. If I camp with my wife, I'll sleep on the "pillow" side, since I'm a side-sleeper anyway. Plus, I'm using two King-size pillows that totally span the head area. Another thing: in the area at the foot of the bed, which the 54" long body pillow doesn't cover, there'll be a soft bag to hold shoes/boots (in case they're wet) and easily accessible (if dry, they go on a shelf over the foot area).
Since then, I have added a second Florvag mattress on the bottom (encased in its' own waterproof cover) as a foundation, even though one was sufficient for my use (my wife asked for a thiker foam base), making the folding up of both layers pretty challenging, so I decided to leave them laying flat, and moved the large cooler to the TV for transport, and use a large plastic tray under the water carriers (in case of leaks) sitting on top of the mattresses (still secured to the e-track).

- 36 x 24 x 8 tray.jpg (16.38 KiB) Viewed 1018 times
As my needs are re-evaluated (with further camping trips), and my modifications to loading the trailer/actual design changes, I'll probably eliminate the iside loading of the cabin entirely.