Half link for 18mm Planet Ocean bracelet? (115ST1589)

Hi everyone, new member on here so still getting acquainted with the forum 😀

So recently purchased my first Omega, a Planet Ocean and it sits a bit loose on my wrist. I think a half link is the way to go as there's no micro adjustment on the clasp. Any advice and where to find an authentic half link, and what to pay?

I'm in Preston, UK.

Thanks in advance.