Lunchables

Further to previous post if you're interested in big finish these are what I would think of as the S tier classics:

Spare Parts: fifth doctor & Nyssa. Standalone but benefits from having seen Earthshock (80s TV story). BF's run at a Cyberman origin story. Absolutely brutal. Hugely influential on new who cyberman material.

Jubilee: sixth doctor & Evelyn Smythe. Standalone but Evelyn is introduced in The Marian Conspiracy if you want to know more about her. Later adapted into Dalek (2005). The Doctor and Evelyn land in the English Empire 100 years after Earth fought off a dalek invasion... With the aid of the Doctor and Evelyn. There is one dalek prisoner and it is set to be executed at the Jubilee.

Big finish can do you new adventures of any number of Doctor Whos

They can even give you Jo Martin

If you're looking for a new era w a new Doctor then I would recommend jumping into the Eighth Doctor audios as there's loads of them. You can start with Storm Warning for a more classic who esque experience OR The Eighth Doctor Adventures S1 for a more new who esque experience

If you're after a totally new thing to get into there's Gallifrey (has some prerequisites. If this appeals to you I imagine you will work it out)

If you're after new stuff that's less classic who oriented another potential jumping in point is actually the Sixth Doctor audios. Due to a quirk in continuity (actually bcos the show was nearly cancelled) he has an almost fully open ended canon and a whole range of expanded universe companions including OG Big finish companion Evelyn Smythe

inspired by this post by @the-macra: