I heartily recommend Destiny Rising[1] by M. D. Cooper -- free on Kindle Unlimited. It's the first 2 books of the "Intrepid Saga", which in turn is part of a growing collection of series in the "Aeon 14" universe[2]. It's really fun and also engrossing.

Some of the related series, like "Perseus Gate"[3] are hilarious. All of these stories have a lighthearted tone and have great character development. They are based on "hard" sci-fi (i.e. plausible inventions) and touch on deeper topics like the meaning of sentience, and of freedom, but they never get heavy.

[1] https://www.amazon.com/Destiny-Rising-Military-Space-Intrepi... [2] http://www.aeon14.com [3] http://www.aeon14.com/series/perseus-gate-season-1-orion-spa...