Choose HIMARI or SORA when the published dimensions fit your room and you can regularly lift, air and keep the bedding dry. Compare the firmer HIMARI with the fuller SORA by personal preference, storage space and the actual local offering. Thickness alone does not determine comfort.
Details to check before choosing
Measure the usable length and width of the floor, platform or bed base, including any raised edges. Compare those measurements with the exact model and size offered for your country. Then check the folded size and weight, and choose a sheet or cover that fits the same dimensions.
After sleep, lift or stand the shikibuton so you can inspect its underside and the supporting surface. Let both release moisture. Air both faces in a ventilated place, turn the bedding over and rotate it head to foot regularly. Fold and store it only when it is dry.
Sources for this answer
Is there room for the bedding between sleeping and storage?
If a Central Valley room doubles as a workspace and guest room, picture the morning after a visitor has slept there. The shikibuton needs somewhere to air before going dry into a cupboard. Check whether that position remains available when work begins, as well as measuring the sleeping area. A room that must be cleared immediately may be easier to manage with a fixed bed.
Compare HIMARI's firmer support with SORA's fuller cushioning. HIMARI is 210 cm long and approximately 10 cm thick overall; SORA is 200 cm long and approximately 12 cm thick. Check the offered width, weight and folded dimensions of your chosen variant. A preference for deep softness, and who can lift the bedding regularly, matter just as much as gaining daytime floor space.
How do I choose between HIMARI 日葵 and SORA 宙? · How do Japanese shikibuton sizes compare with local bed sizes?