Ultra sonic mister or warm mist humidifer?

Please HELP!!!!!! i have had/have a spider mite problem which i am currently useing Nurse Naam oil and misting 3-4 times aday underside of leaves but now some of my plants are looking really droopy and there are still sign's of spider mite damage but only 3 out of 30 plants have still have them on before i spray them off i have got my temp to 72f-81.4 and bought a humidifer(ultrasonic cold mist) but my humidty is still only 33-44% over than when mist continuasly when it goes up to 65%, i run my lights at night to keep temp roughly ok but this is hard work to keep the right humidty so anyone has info on a cheap but decent humidfer thanks!! p.s i live in the U.K