Entry-level model for small puppies or dogs Mini

I bought this backpack for our Parson Russell puppies. He is now 4 months old and can not walk so wahnsinning long course. But since we want to go for a few days to Denmark there much go for a walk, I wanted to make sure that we can wear it nice and warm just in case. I had read a lot of reviews before buying, and a more accurate indication of size missing, for the animal to be transported; hence my now:
Our puppy is now 28 cm high and 30 cm long (from shoulder to tail) and fit just so into this backpack. Since this is not so crazy expensive, the purchase for a relatively short use is fine.
As a transport box we have before buying the puppies they worried: Foldable, blue transport box for dogs 60cm x 42cm x 42cm from Pelzi because we also wanted to take advantage of when he is fully grown.
When starting box, the backpack of Trixie had super enough, because the shipping was of course much too large. However, we are probably the backpack can no longer use so incredibly long.