A. You might be able to find a tube that will cover both sizes.
B. I've used Shimano M520 for a few years, double sided - no problems:
https://www.youtube.com/watch?v=FFyX...6zPoymgKaIoDLA
C. I'm currently using a Scott Tour on my folding bike.
Size 9.5/43, paid less than $100:
https://www.youtube.com/watch?v=Fh5V...6zPoymgKaIoDLA