One thing to consider when buying tubes is ease of installation, particularly when you have to switch the tube out on the road. It can be really difficult to install a wide tube in a narrow tire even if it might work. When I purchase tubes for the 700C X 23 rear tire on my recumbent trike I always look for ones that are rated for 700C X 28 to 32 over tubes rated for 700C X 32 to 35. The difference seems small and both tubes will work OK but it seems to be far easier to get the narrower tube in the tire quickly. As far as loss of air as the tire sits, it doesn't seem to make much difference.

A very good tutorial on tire size: https://www.sheldonbrown.com/tire-sizing.html