I would go back to the 0.6 coil. Is your nic salt juice all new? What m.g. is it? Unless it's crazy high (higher than your prior juice) the whole "nic salt and special equipment" is just nonsense. You can use nic salts in sub0hm equipment at the right nic level which is what is key. Most folks don't have issues with 3 or 6 mg freebase, so unless someone is SUPER nic sensitive, they won't usually bother.
Nic salts are smoother, meaning they can be mixed at ungodly percentages. So, unless your salt juice is 45 mg/ml and you were at 24 mg/ml of freebase, the salt juice will not care what coil you use with it.
The 0.6 coil is going to (probably) emit more vapor per puff, but if your nic level change was 1:1, meaning you haven't increased it, there is no reason not to use the coil you prefer. It won't harm the coil, you should get approximately the same life out of it that you were getting.
However, if your nic salt is MUCH HIGHER than you were using, I'd say either go down in nic strength, and stay with the coil that works. It's going to work out better for you in the long run than burning through the other coils in a couple of days.
The whole "nic salt" capable device/coil/etc. it's just "marketing" of the newest, greatest craze in vaping. It's, for the most part, nonsense.
What matters is you aren't overdoing the nic, period, and that is all. You would be at higher risk of nic overload using a much higher nic level and the same coil.... Well, don't do that. If you want salt juices, get them at the level that was working for you before (or, slightly higher if you are feeling nic deficient).
Your body should tell you: nausea, shaking, dizziness, headaches, hiccups, yawning, fatigue if you are getting nic sick long before you would overdose. It's really almost impossible to do as long as you keep those general principles in mind. Etc.
Best of luck,
Anna