The usual recommendation for brushes are sable, such as Winsor & Newton 'Kolinsky Number 7' range, but I'm not keen on them. I find them a bit too soft, and tend to show wear fairly soon, no matter how carefully I look after them - or perhaps that's just me?
My preferred choice is Winsor & Newton 'Sceptre Gold 11'. They are sable - synthetic mixture, with very a similar performance to all sable, but slightly springier/stiffer, and more resilient
Also for detail painting I use Winsor & Newton 'University', which are all synthetic, and springier again, but still a usable paintbrush
Typical prices for a size 1 are - #7 = £9 or £10; SG11 = £4 to £4-50; Uni = £3
For detail work you will want the smaller sizes. The very fine brushes are sized 00000; 0000 etc, up to 0, usually written as 5/0, 4/0 etc, plus size 1. You don't need the full range, perhaps missing out some of the ?/0 sizes
However, there's only one way to find out what type and size you like, and that's to try a few, but I would include some Sceptre Gold 11
They are available from The Range hobby & household stores, or Surf t'Net
Also, have a look on t'Net & YouTube for 'Masters Brush Cleaning Soap' - it's excellent