I have a couple of rangefinders ... one is a Voigtländer from the 1950s that matches the Vito II body ... but I find I use them only rarely.
With the Rollei 35, in good light I set the camera to f/11 and use the distance scale. All you have to remember, really, is 2m (6') and 6m (20') for near and far subjects. For distances up to 6' with larger apertures, it's easy to measure the distance with your arms and hands (although it might look a little funny...
): learn how long your arm is, your forearm, the width of your hand, the width of your finger span, and use them as rulers. As distances grow between 6' and 18', learn the sizes of common things around you (like flooring tiles, window sizes, the length of a park bench, etc) so you can gauge distance by just looking around you and assessing what things
are between you and the subject.
If you do it enough, it all becomes natural and easy. This means: load the camera, shoot 36 photos within a day and remember how you measured the distances, process the film IMMEDIATELY and look at the results even if only on a light table with a magnifying glass so you can confirm whether your focusing method hit or miss. Then learn when you make mistakes and remember it, go shoot another roll the next day, or as soon as you can, and do the same thing.
The focusing problem is greater when I move to 6x6 because of the larger format's much shallower DoF. I practice scale focusing with my Polaroid SX-70 for that format: it's a similar sized format and you find that f/8 to f/16 does not net anywhere near as much DoF at the usual distances so it's easy to see the differences between getting it right and not. Estimate the distance first, then focus the SX-70 using its viewfinder ... check to see whether I got it right.
Having a good RF or tape measure to get critically accurate focusing is nice, but some effort and practice to learn scale focusing and DoF technique can go a very long way and make using the external tools much less of a priority. It's just like learning how to guesstimate exposure...