If you're fine with sweet potatoes and courgettes (zucchini) then also try carrots, cucumber, melon. You might be able to cope with swede and turnip too, though since you've reacted to other brassicae it might be worth being cautious there. I agree with sbhikes about thorough roasting and stewing.
Please read my response in the Gut Healing thread:
In addition to the suggestions there, well cooked veggies are easier to digest than raw or lightly cooked. You might also want to try adding in some digestive enzymes and maybe some HCL (you can get some digestive enzymes which have HCL in them) to help your body break things down.