What is good for firming up stools on french bulldog for long term

As I stated I have a 11 month old frenchie and ever since I got him his stool aren't very firm, I have tried everything, he was on purina pro plan and now i switch to blue buffalo, it helped with his farts problem but with his stool still soft, it isnt diarrhea it just soft and theres always leftover on his behind which is a hassle when he goes outside then comes back inside we have to see if he's dirty or not, i have given him rice and pumpkin puree with his food and it helps a bit but still some poop on him, what can i do on the long term so everything comes out good so it dont get stuck so i wont have to clean him everytime he uses the bathroom, i also have a chihuahua and he been on blue buffalo since a puppy and no issues at all with his stool, thank you for reading hope someone can help me