Bed sharing with Emma mattress

We've got a similar mattress and never had any issues. I follow all the safe sleep advice around blankets and whatnot.

If you're super worried about it just get a cheap but firm mattress from somewhere like ikea for £200ish. They've all been through the same safety testing.

My mattress isn’t incredibly firm and I cosleep with my 6 week old. I sleep stomach to stomach with her on the inside of the bed rather than the outside so there is less of a dipping from my weight to stop there being any chance of her rolling over x

You'll have to decide as a family what you want to do. You can take the (small, but nevertheless there) risk of continuing to use the mattress, or find a way of getting a new/secondhand one, or get little one a bedside crib to sleep in instead.