I am not an expert, but I would say memory foam is the best option. Yes, as been mentioned above, they are rather expensive, but it is not bad investment in your health. Moreover, they're rather durable and can serve 10-20 years easily, at least most of manufacturers provide with 10-20 years of official warranty, I guess it is a good sign. If I still couldn't convince you, check this source with the most detailed review on modern mattresses https://sleepissimple.co.uk/ . While choosing one, please take into account the next factors: Price, support, comfort, level of firmness and longevity of the warranty from manufacturer. Good luck!
I wouldn't go for memory foam if you get hot in bed, I don't but if I sleep on memory foam my hair and back are drenched in sweat. Better off getting a topper if you want to try one out, or just trying out comfortable mattresses would be better if yours is old and unsupportive. Could also try hot and cold therapy and using core muscle exercises to help stabilise that part of the body.
Sacroiliac Joint Pain is one of the best common complaints that people bring to their doctors. Nowadays 80% of adults are suffering from back pain and joint pain due to sleep. Research shows that there is a relationship exist between sacroiliac joint pain and sleep. The most important thing due to which most of the people are suffering from pain is bad quality of the mattress.
According to researcher matelas futon is better for you, if you are suffering from joint pain as well as back pain. While you have to choose the best mattress for your bedding also keep these points in your mind such as price, support level of comforts, longevity, and warranty.