Upsizing Solar PV system

We have a dual battery system in our Landcruiser Troopy camper, powered by Solar PV. We originally bought an 80W (4x20W) mono crystalline system, but this was not enough for our fridge and computer charging when we were in Tassie last year.

We expanded this with a 40W semi-flexible panel (bought over the internet), and this gave us enough charge most of the time, depending on clouds and shade. After almost 1 year, the 40W panel died, and there was no response to our emails about this from LenSun HK.

So now, we need to upsize the system once again. I have seen articles and comments that additional panels need to be 'compatible'. I am also thinking about where to store the extra panel/s...

My questions:
- What is 'compatible'? My current mono crystalline panels each output ~20V and 1A = 20W. Should any new panels also output ~20V? Should they be mono crystalline? Can I incorporate the new fully-flexible panels onto the same charge controller?
- What are your experiences with the semi-flexible panels? They take up less space, but how reliable are they?
- Where is a good place to buy 20W or 40W panels?

Happy travelling
Rob