You could try an xpen or a puppy pen, have a pee pad in one corner & bed/food/toys in the other, that way you dont feel like your trapping the puppy in a small cage
this worked for me with my pup. It also helps to not let them roam around too much cuz thats when they take the oppertunity to pee/poop!
I also ordered a dna test off amazon for mixed breed dogs for my shihtzu/pom mix and his family tree confirmed he was 50/50 shihtzu/pomeranian. It was really helpful and definately helped me learn more about him and link his behaviors to his breeds.