My wife and I have cycled twice in Slovenia, both as seniors (early 60s and 70s). First time in about 2014 with a Slovenian company (Trek Trek) renting their bikes and having them haul luggage, and then on our own in 2017 with touring bikes we brought with us on the airline. We hauled clothes etc. in rear panniers and handlebar bags (no camping involved). The commercial tour (self-guided) involved a good deal of climbing, as the route essentially circled the Julian Alps (over Vrsic Pass) and then wound its way down to Piran on the coast. The Soca Valley was relatively flat if I recall correctly but there were mountains at the north end (the alps) and then hills (wine country) at the south end. On our own touring bikes we rode from Kamnik over a modest pass (I recall only one short steep section) to reach Ljubno ob Savinji (40 km) a neat little village on a river, to Logarska Dolina (30 km), a beautiful, quiet valley with hiking trails into the Karavanke Mountains. From LD we road to Celje (80 km, mostly downhill or flat--we did it on a rainy day so didn't see much of anything). Celje to Ptuj (42km ?) was also mostly flat or modest hills. Almost all of this was on roads, some with little traffic and some with moderate traffic. Back in NW Slovenia, the Radovna Valley between Bled and Kranska Gora is a short (15 km?) delight, but there are a few hills to get to the start (from Bled) and a short, very steep hill (we may have walked up it) toward the north end. There is a good "rails-to-trails" bike path between Kranska Gora and Tarvisio Italy that is 20-30 km long. The route between Villach, Austria and Tarvisio is also a day's ride and not difficult. I can dig out actual distances and provide where we stayed if it would be helpful. We did a lot of clothes washing in the sink associated with our room.