I used to use Fimo and used to reinforce some delicate items with perforated aluminium sheet they use for car repairs. Fimo can be quite brittle unless thick and chunky, but curing it in an oven helps. Make sure you use the correct temperature. Did send some quite fragile dragon models to Australia once, with the reinforcement, and they arrived safely.
Made the mistake of asking my partner to “cook” some Fimo models I had made, while I had a bath, and came down to see the kitchen full of smoke. She had misheard the temperature setting I gave her, and dialled- in almost double the correct temperature, and the oven was never the same again ! I think the fumes were toxic too at high temps.