Without a shawdow of doubt I would use Nature Diet puppy (wet)
Toilet is always in our case firm - (sometimes a little too). Was recommended this by a top european soft tissue specialist who I was first referred to with Miststy - we arrived at this one after many tests - and although Misty was a a special prescription food costing £2 per can she actually did better on this. They do have several recipes i.e puppy, sensitive, etc and will send you samples if you email them.
regards
sue