For the heat-sinks I just used the supplied thermal tape that comes with them, they get hot so they must be doing something; the black heat-sink was supplied with the case, I had already got the silver CPU heatsink from Pine with the Rock 64 board.
Using
cat /sys/class/thermal/thermal_zone*/temp
the board was reporting about 77C before the assembly, and about 50C after, so thats a pretty good improvement. I got the case from Amazon UK for just under £10.
I would say just good luck for the future.