I'm struggling to understand the differences between a 960 and a 1060. Is it that the 1060 has twice as many radios so it can transmit on both at the same time?

I've not looked at the 1060 before but a quick read of the Draytek specs shows that it and the 960 are very different beasts. If you don't understand the differences are you sure that one of these is what you need?
One might think that the "extra" radio would be used for a dedicated backhaul link in the mesh, but it seems that that is not the case, and it's used as a "monitor" for channel interference....

Confusingly, it seems the 1060 can also be used to manage other APs, in which case it is designated as "root", although this is nothing to do with "root" and "node" in the mesh setup

They could have come up with a clearer nomenclature....

If I understand it correctly the 1060 has 5 radios, one for monitoring, 2 x 2.4GHz and 2 x 5GHz? Whereas the 960 has 1 x 2.4GHz and 1 x 5GHz? I'm assuming the extra radios on the 1060 are used for making a mesh connection? I assume there is little benefit in having two identical SSID's on different channels at 2.4GHz or 5GHz. It's not helped by the fact the 960 has a downloadable datasheet but there is not one for the 1060.

I'm not sure where you get the idea that the 1060 has 5 radios? The specs say that it has AX3600 capability (vs the 960's AX1800), it has the potential for 8 SSID's per channel (vs 4 on the 960) and has a 2.5Gb LAN port (vs 1Gb on the 960). As said above, it would seem that the third radio is not used for the mesh.

https://www.draytek.co.uk/products/business/vigorap-1060c/#specifications

https://www.draytek.co.uk/products/comparison/wireless-ap-comparison