OK. In Prime, I designed Typography scale that may be used for Desktop and Mobile.

When you create mockups in Sketch, you add separate artboards for various device types (all at 1x scale). You can apply multiple sizes of fonts to match the need of a particular platform. There is no simple method of making one artboard that resizes (in terms of RWD) directly in Sketch. There is a plugin called Pointbreak that tries to simulate that.

Hope this helps.