Just add to what Wardy has said; If you use illustrator or other vector software, you will be able to blow the images up as large as you like. If you use photoshop you will need to determine the final maximum size when you first set your illustration up. You can make pixel-based images smaller, but if you increase their side from the original they degrade.
I am guessing from the samples you have used, that you are looking to make something for your child’s bedroom wall. One other thing to consider is that with for this sized illustration, the file size would be fairly huge if you use photoshop. With illustrator, (et al), the file would be fairly small and be easier to work with, especially if you don’t have a particularly high-spec machine.
A good alternative to illustrator is Serif‘s Affinity Designer. Much cheaper too.
If this is just for a one-off project, the alternative, of course, is to go on to behance, find an illustrator with a similar style and employ them to do it. It may be cheaper and easier in the long run if you factor in the time it will take you to learn. It will be a fairly steep curve if you’ve never done it before. There’s this illustrator called Wardy…