Also see Hello toothpaste (not affiliated) which has fluoride but not SLS: https://www.hello-products.com/products/naturally-whitening-...

Same problem for me, constant canker sores. Switching to Hello hasn't totally eliminated them, but it has reduced them.

If you don't mind a baking soda toothpaste, then another option is Trader Joe's. They made a baking soda & fluoride toothpaste that is SLS free. Been using it for a number of years now... Though it's been briefly discontinued and is slated to be back later this year.

Burst - https://burstoralcare.com/products/toothpaste-fluoride

Also Native has one too.

Sensodyne is one that's readily available at most stores.