Proper soft starter for vacuum cleaner universal motor
You'd better to make something more hi-tech if you intend to make a PCB board abd embed into a machine.
Today these motor controller are made with tinny MCUs, but some decades ago they were made from specific IC made from Telefunken, Temic, Siemens, lastly from Atmel. The U2008B would solve your demand. Probably you can still get some ready made board with potentiometer to adjust speed, Google is your friend.
EDIT:
If your motor is equiped with tacho (speed sensor), then there are also bunch of TDA1085C boards lying arround.