Deficit recommendation?

Hey all, I would love some recommendations.

I'm 19, 5'7" and weigh 144 pounds. I'd like to get down to 120 (obviously as soon as possible). Because of heart and lung conditions, I am unable to do HIIT/extreme cardio, so I do strength training on a low intensity. I also am a student, so most of my time is spent (ugh) sitting and I am required to have a (nasty) meal plan.

That being said, can I have a recommendation for caloric intake? I'm thought to be mesomorphic and I do about 30 minutes of light exercise 5x a week.

Thanks for all your brilliance.