We plan to stay near the centre of Ljubljana at Kollmann Rooms. Any recommendations for reputable car hire that is within walking distance?

We had an easy rental in Ljubljana in 2019 through Auto Europe. www.autoeurope.com. If you aren't familiar it is an arranger with many large car rental agencies. I don't remember exactly what agency but one of the big ones. The office was at a central hotel. Some other agencies were available at the train station but that was more convenient for us staying near the river. With google maps was easy drive out and back for the day.

Thanks for that info. I’ll have a look at that site.