I just use 23C tubes for tyres up to 32C width. Smaller weight and volume (and often cheaper in bulk from somewhere such as Torpedo7), and despite people's unfounded fears, I haven't had any issues in around 10 years of randonnee and touring and commuting riding using the smaller tubes.

The real issue for touring is to ensure that the tyres are pumped up to a decent psi. Under-inflated tyres cause pinch flats and we had a couple of those in Japan because of the high lip on driveway crossings. The reason was that I deviated away from my usual tyre pumps to another brand, and those pumps would not get to a decent pressure at all; they were a curse throughout the trip.

Anyway, my advice would be to get expert in feeling your tyre pressure (most people think their tyres are pumped up enough when they use their fingers to test, but in fact the tyres are at half pressure), or invest in a Zefal tyre pressure gauge, or invest in a Topeak pump with the gauge included.

Oh, and look at the highest pressure spec on the sidewall of the tyre. and if you go to a wider tyre as per the other thread, readjust your bike computer to the appropriate circumference setting.