Did it for the first time this summer, in Iceland. Was initially very strange, mainly changing gears with the wrong hand (I tried to open the car door first time I tried to pull away), but I got used to all very quickly. Only once in three days of driving did I mess up and drift into the wrong lane coming out of a junction, someone honked behind me and I sorted it out (thankfully the road I was pulling onto was empty).
Did it for the first time last month, in a rental. It was mostly fine after I stopped driving so far over to the right that I was basically on the hard shoulder.
if you’re in a right hand drive car it’s totally fine. you get used to it in about 5 minutes. if you’re in a left hand drive car, it’s a bit annoying but also totally fine. but your brain will play tricks on you whenever you come to a junction with no other cars
We got in to the habit that every junction we got to I would say out loud “I am driving on the right” and saying what I was doing. It particularly helped with not going the wrong way round roundabouts.
if you cover up the passenger’s half of the windscreen with a large piece of black card you can just focus on the road in front of you and not worry about sides.
I scraped a Ford Focus hire car against the side of a bus in Perpignon about fifteen years ago, but have driven since with no issues. Just make sure your pickup point is somewhere that isn’t in a mad city centre where you’ll be forced to figure out the traffic system and a left hand drive at the same time.