Lesley has been helping me and has been a great help.
The problem when migrating from Prestashop was that I had so many poorly written modules with so many fixes over the years just to keep it working, that when I migrated to thirty bees, all these problems were carried over.
So rather than migrating, I'm going to do a clean install of thirty bees and then just copy over the data I need from the database. I think this is a better way of doing it if you want the true benefits of thirty bees and leave behind all the nightmares of prestashop.