For understanding Entropy and Heat,
I recommend H.B Callen's https://www.amazon.com/Thermodynamics-Intro-Thermostat-2E-Clo/dp/0471862568
Thermodynamics and an Introduction to Thermostatistics 2nd Edition
I'm *sure your local library has a copy of it. I recommend looking for a copy at the Library of Genes.is. (hint hint).
There is a classic textbook for thermodynamics: Herbert Callen - Thermodynamics (https://www.amazon.com/Thermodynamics-Intro-Thermostat-2E-Clo/dp/0471862568/ref=sr_1_1?s=books&ie=UTF8&qid=1548031799&sr=1-1&keywords=callen+thermodynamics). Depending on the complexity level you're looking for, you could go to pretty much any undergrad level textbook, or you could go straight to statistical mechanics, which is basically a generalization of equilibrium thermodynamics. Is such case, there are a lot of good textbooks on SM, but Reif's Fundamentals of Statistical and Thermal Physics (https://www.amazon.com/Fundamentals-Statistical-Thermal-Physics-Frederick/dp/1577666127/ref=sr_1_1?ie=UTF8&qid=1548032034&sr=8-1&keywords=reif+statistical+and+thermal+physics) is classic too.
Nothing but run of the mill textbooks? Good heavens!!! The Physics and Chemistry of Color, K. Nassau and Thermodynamics and an Introduction to Thermostatistics
Look outside the box.