Looking for feedback on minimalist DIY build with wool comfort layer

Hi all. I've been considering a DIY build mattress for a while to replace my sagging ~5 year old purple mattress.

The customizability and ability to replace parts is why I'm interested in doing this route.

I'm 5'9 and 148 lbs. I rotate basically all sleep positions, but I suspect this is partially because my current mattress sags uncomfortably. I think ideally I'd stick to back and side sleeping, but both are kinda painful currently. I also have lower back pain caused by degenerative disc disease, so having quality, long lasting support is very important to me.

I'd love to try to recreate a pillow top type setup. I found this wool topper that seems to check all the boxes, and I suspect will help with possible temperature regulation issues from latex. Here's a pretty minimalist build I'm thinking about trying:

• 3 inch firm support layer of dunlop latex https://www.amazon.com/gp/aw/d/B00UYG9F4C/

• 1.5 inch wool topper: https://www.amazon.com/gp/aw/d/B004DC1S2K/

Do you have recc's for the firmness level of the latex layer? Should I add some medium firmness latex in between as a transition layer?

Any other feedback on the build?

Thanks so much!