Size of laminate flooring expansion gap
Leave the recommended 3/8" clearance gap.

Install your baseboard gently down to the flooring material. If there are minor swails in the floor surface the baseboard may very well leave a vertical gap up off the surface the the flooring material. The way this is normally dealt with is to install base shoe molding. Base shoe is a narrow molding which can easily bend down and follow the floor surface variations.