There are standard product CXL memory expander chips if you don't want to design a custom chip.
https://www.marvell.com/products/cxl.html
there's multiple vendors even https://www.asteralabs.com/products/leo-cxl-smart-memory-con...
there's multiple vendors even https://www.asteralabs.com/products/leo-cxl-smart-memory-con...