You can look into buying the hospital type bed frame for her.

https://shopee.com.my/product/1057873/380383313?smtt=0.0.3

As an older person, normally we want medium firm - firm mattresses. Avoid the soft mattresses.

However it also depends on your mum's personal preference as well as how severe the curve is. 100% coconut fibre isn't really good if the curve is severe, so you may want to look at the hybrids. My friend has a hunch over, and he uses some pillows to help support.

If possible, maybe can buy one hybrid mattress and ask her to try? If it doesn't work then go for something firmer or softer.

Highly recommended this one. https://www.facebook.com/ECOluxMattress

You can thank me later. Already bought 3 mattress from them. 2 Kings and 1 Queen. Hidden gem in the local scene.
Best part, it's really affordable even for king and queen. Don't just take my word for it. Give them a pm and you will understand what I say