+ another 1 here for the Mirka hand sanding block with vac connection, + their abrasive sheets in various grades - all for flat work. Quite pricey but worth it, and here anyway, you have to search a bit to find the finer (above 180 grit) variants - here anyway.
And if you want discs for a ROS, their abrasive is excellent too, but in my experience you MUST use the foam "inbetween" pad, otherwise the edges of the disc get ripped off long before the abrasive is worn away.