Designing custom solenoid with feedback for measuring force
I believe you can easily achieve 0.1N in a HDD rotary voice coil motor VCM using rare earth magnets and precision bearing actuator.   Current can be used for feedback as well as rotary encoder.  You just have to make it fit and find the sources for parts.

The main problem with approach is calibration, and thermal weakening effects.

Comparison of miniature Linear motors, moving coil vs moving core.

. . . . . . . . . . .     Voice Coil Motor . . . Solenoid


Force . . . . . Low to medium  . . High
Stroke . . . . . . . . 5 inches max    . . ~ ¼ inch 
Constant Force. . . . . .  Yes     . . . . No
Reversible . . . . . . . . .Yes    . . . . .No , yes without spring
Position/Force Control . . . Yes   . . No
Cost   . . . . . . . . . .Moderate     . . Low