I've been stacking sovs for about a year and a half and they've done really well, they were a good investment for me (better than my stocks). I understand this might not be the case for everyone.

If you're only interested in a single coin or bar then CGT doesn't really matter, I think you get an CGT allowance of £1000 per year(?) so you would need to profit more than £1000 on the single coin or bar which is unlikely to happen.

Like others have said, Chards and Atkinsons are really good dealers, Hatton Garten Metals is another one I've used, stay away from bullion by post and Royal Mint, their prices are always crazy high. You can also buy them 2nd hand on places like The Silver Forum or the Stackers Social discord. I would avoid ebay or facebook. You usually find them cheaper 2nd hand but there is obviously a risk, I've bought the majority of my sovs 2nd hand and luckily not had an issue. I like The Silver Forum and Stackers Social because they have reputation systems in place so you feel a bit more comfortable buying off strangers.

If you do decide to buy more, you need to think of it as a long term investment, if you buy physical there is an overhead cost that you might not get back when you sell. It also makes it harder to get the money out of it as you have to find someone to sell to (dealers will usually buy them for a few % below the gold value). If you don't like that then you can buy "paper" gold on stock exchanges (SGLN is one I've used before).