What kind of transistor do I use for switching high voltage with a microcontroller?
NPN is correct transistor type BUT load MUST be in collector.
That way low voltage at Vbe drives the base, and the collector switches HV. 
The transistor must be rated for usefully more than 90 V.
See www.digikey.com selection guide.
MPSA42 was the olde time favourite at about 300V rating. 

With load in the collector the circuit inverts - ie Vin high = on. 
Whether this suits depends on your need.
This can be altered to Vin high = off with additional components. 







simulate this circuit &ndash; Schematic created using CircuitLab