If you're losing coolant and it's not going on the ground, it's going somewhere . . . . and I suspect it's going into a cylinder and being burned.
The way you describe it it appears to be a slight/slow loss . . . maybe a head gasket just starting to go. If you're getting coolant in the oil (which you say you are not?), then that may be an indication of a lower cylinder seal going . . . although that's pretty darn rare, except in botched rebuilds and then it shows up right away . . . . and usually a lot.
One thing you DON'T want to have happen is vent coolant (glycol) into the oil. Glycol will displace the oil on bearing surfaces and cause VERY rapid wear. If you get coolant in the oil, change the oil & filter right away, run the engine for a bit, then change it again to try and get ALL the glycol out of it.
As long as you're confident you're not getting coolant in the oil, then I guess you can keep on driving it . . . . but not too far from where you want to tow it from.
I suppose you could test the system by removing the spark plugs and pressurizing the radiator to try and vent coolant into the cylinders where you could see it. In the end, however, you may be stuck on a new head gasket. My advice would be to do it now at your leisure rather than later at maybe not your leisure.
Like I said, if you're losing coolant and it's not on the ground, then it's either going into a cylinder or into the oil pan.
Do a compession check now.