Luggage Fit for Travelling Around Thailand ?

[jaizan]

For years, I have used a rucksack.     About 80l capacity. 
This means I can walk up and down steps & have no problems with the rough pavements found in Thailand & nearby countries.
The downside is it can be a bit sweaty at times.

 

I think I'd like something which has the option of using a rucksack or wheels. 

The first thing I note is small wheels.   Wouldn't larger wheels be preferable on Thai pavements ?
Then most of the products I see are lower capacity.

Note, I will typically take public transport from Suvarnabhumi to my hotel.   Or from regional bus & train stations.    So there is some walking with the luggage.  I'm fine with that, but the luggage needs to be up to it.  .