But, it wouldn't be practical to leave out the Latin entirely. I can understand not wanting it as a focus. But to use your "theatre" example, Latin and French are indispensable links between Greek and English: θεάομαι > θέατρον > L. theatrum > Fr. theatre > E. theatre/theater.
If you can't find a book that focuses on this, you can learn a lot just by studying Greek suffixes and word formation (such as the -τρον suffix mentioned above).
Paying some attention to Latin also helps in spotting false cognates: e.g. it makes it easy to see that κοίτη and "coitus" are not related.
Dic mihi, Damoeta, 'cuium pecus' anne Latinum?