Krugman is the best-sounding stuff of the mainstream. Since that what you brought up, I would start with https://www.crisesnotes.com/paul-krugman-functional-finance-... . Arguable Krugman is so good about not saying terrible stupid shit, that it might come at at cost of not being internally consistent or acknowledging when his views in fact change.

Krugman at least was a "New Keynsian", which is a very complicated confused thing in the way the neoclassical parts and keynesian pieces are mashed together. I mostly subscribe to the Post-Keynesian stuff, which makes a lot more sense to me, and is more embracing of the weird/humanities side of Keynes. https://vebaccount.substack.com/p/the-post-keynesian-worldvi... is a good primer, and really that person's entire corpus is a gem of really good writing. For something that (at least in the last few years) is much more grounded, try http://jwmason.org/the-slack-wire/.

Now you might say that the opposition's views of the mainstream is an unfair place to begin. To that, I say just look at the shit Larry Summers says.