I have some flat faced mdf baseboards that have been primed with a couple coats of white zinsser BIN shellac primer. The BIN primer has been Sanded so smooth that it feels very slick like glass to the touch. I will be painting the baseboards with Benjamin Moore Ben latex paint. I do want a super smooth finish but fear the surface is too smooth for the top coat of paint. What would you suggest I do? Should I scuff sand the surface? What grit should I use? I tried scuff sanding with 220 but it still feels super smooth.  Sanding with 150 also feels smooth but shows sanding lines through the paint.  Thank you so  much for your help and I really appreciate it!
Please take care and stay safe.Brad