Hi Glasswelder,
Welcome to the mattress forum:).
I am sorry to hear your partner has scoliosis. We have had people write about this in the past. A forum search on scoliosis (you can just click the link) will bring up all the forum posts and topics that mention it (along with any linked posts that mention scoliosis in the title) but I would always keep in mind that there is no such thing as a mattress that is “best for scoliosis” or any other health or medical condition … there is only a mattress that is “best for YOU” or your partner, in terms of comfort, firmness, and PPP(Posture and alignment, Pressure relief, and Personal preferences). Each person is unique and a mattress that is perfect for one person with scoliosis may be completely unsuitable for someone else with scoliosis to sleep on if they have a different body type, sleeping style, sensitivities, preferences, or differences in the severity of their scoliosis.
The steps involved in finding the best mattress for anyone with any specific health or medical condition would be the same as my reply in post #2 here and are also the same steps as choosing a mattress for someone that has no health or medical conditions because the two main functions of any mattress that would apply to anyone are to keep your spine and joints in neutral alignment (whatever that may be for you or your partner) and to provide good pressure relief in all your sleeping positions.
You can also research Trusted Members and talk to them about what they recommend, at least you will get professional service and knowledgable staff that wants to help.
Good luck to you and your partner.
Phoenix