This is something that has been bugging me since '10. Strings that bite into your finger. Here is something you can try if you like the performance of one type of string, but prefer a different kind of string for your slipknot.
I present to you, the Blood Knot, a common knot in fishing used to join two lines of similar size.
I’ve tried this a long time ago on yoyo strings, and when done minimally, you will hardly even feel the knot in the string, and you can place it very close to the slip knot. Basically, this allows you to use a soft, comfortable string for your slip knot and a performance string for the rest of the whole. This is also possible on swivels, but the reason I was reminded of this is because I wanted the double-type string without the use of a swivel because I had a raw yoyo.