Olly D wrote:
My problem is that I'm nervous of using compression fittings.

Then just get on & use some. Such diffidence will be replaced by
confidence.

As I can solder, is it possible to mix the
fittings, for example could I use an end feed tap connector on the
compression ball valve? The threads look the same...

If you can solder, you can use two spanners. Look up the manufacturers'
website if you need instructions on how to make a compresssion joint.

Mixing compression and tap connectors would be a bodge; use compression
olives on compression fittings.

The tap connector is a parallel BSP thread and the sealing is by a
compressing the fibre washer between two flat faces. The compression
fitting won't have a suitable flat face.

Different manufacturers of compression fittings use different threads.
Some use BSP threads, others use a finer metric thread.