I bought one of the flasher relays from Amazon linked above and it works great.
I did find it very difficult to get the original relay out. It’s quite awkward to get to and grip. I couldn’t budge it by pulling and jiggling just by hand. I was a bit bothered about damaging it as it seemed stuck tight. In the end I did manage to get it out using a small plastic stick to alternately lever it up on one side then the other, doing this a few times eventually lifted it up enough to pull out by hand.
In case it’s useful to others who want to try this, the reason it’s so tricky to get out is that there are are two plastic wedge tabs on each side of the relay connector on the car. The relay unit itself has a flap with a slot on each side that the wedge tabs on the connector lock in to. I guess if there was a way to lift the relay unit flaps outwards then it would be a lot easier to release, I can’t see that there’s space to do this though, but otherwise some careful alternate levering will do the trick.
Below shows the relay side flaps that the above connector wedges slot into.