Hi Roo
I am sure you got this foam sorted by now but just in case other readers are looking at doing the same this is what we used to do in my industry when doing tool foam boards for the roll cabs.
If you get 5mm sheet as the bottom sheet
Then a different colour 10mm sheet for the middle sheet trace out the shape of the tool you want to put in it, Cut out the shape using a sharp knife (Hardest part is keeping the blade at 90' to the foam)
Then get a 5mm sheet the same colour as the bottom sheet and trace round the item again and cut it out
Then using a spray friendly foam glue, Glue the sheets together to make the foam silhouette
This then gives you a total thickness of 20mm overhaul
Great Idea to blag it from Curry's once you can get pass the H&S person 😂