You may like to have a close look at the one pictured here.
Bearings for home made linear
A good design in my humble opinion.
notice the lateral ajustment screw on the right side only.
It allows for a slight adjustment of the bearing pressure this
is really all that is needed the rail represents a fixed distance
and you only need maybe a little oversize mounting hole giving
a few microns for ajustment.
A further improvement of this design may be to get rid of the nuts
used for spacing out the bearings and making some dedicated
spacers that take better advantage of the bearing shoulder surface
and provide a wider support on the other side.