Hello! I love providing information, so here is some:
It’s difficult to come up with recommendations without knowing you well, but here are some Doctor Who books that I have enjoyed:
Now We Are Six Hundred : a humorous/parodic anthology of Doctor Who related poetry.
The Scientific Secrets of Doctor Who A short story anthology/popular science nonfiction hybrid that contains short stories from the perspective of multiple Doctors based on science, which also includes information on how science has affected the creation of Doctor Who in the real world.
The Day of the Doctor novelization. I remember that when I first heard someone reccomend this one, I thought “Novelization? Isn’t that just a rehash of the TV story?” Nope, this novelization is a transformative experience, turning a good story into a great one, adding interesting new elements, and reinterpreting old ones. It may in fact, be worth your money, even if the idea of a novelization does not appeal at first.
For audios, instead of providing specific titles, I will instead give you advice on places where you can stream them for free. Spotify has a large selection, such as the first 50 stories in the Main range (two hour serial style stories that follow classic Doctors). The BBC sounds website/app also has some stories that you could try (Thread where I provide links):
Free Big Finish Audio Dramas on BBC Sounds!
Also, I just tried the Into the TARDIS podcast today, (which features Colin Baker, Sixth Doctor actor, as host). The promotional podcast features full length Big Finish stories like the examples above, but with an even wider spread of stories available, so you can see what you like.
The “Available for Free” filter (accessible through profile dropdown menu “My Account Settings” > “Customisation” scroll down to “Filters to Include”, drag over to active filters side) can provide more examples of audio stories and other stories that are available for free.
Other stories may be available for free depending on your circumstances, and I would also recommend checking your library system for additional Doctor Who titles you may enjoy.
Did you know that as an American (or at least one who is US based), you can stream most classic Doctor Who episodes for free with ads on Tubi?
https://tubitv.com/networks/classic_doctor_who
I hope my treatise does not overwhelm you, but if you have any questions about this information, you can ask it on the forum, and I or someone else will likely answer your query.