I'm working on an edition and translation of inquisitorial documents from the first 30 years after the creation of the inquisitio heretice pravitatis (inquisition into heretical depravity) in 1230's. This is what is referred to as the 'medieval inquisition', as separate from the later Roman and Spanish Inquisitions.

There are two types of records you can refer to: medieval inquisitors' manuals and depositions of witness statements. Inquisitors were law- and theology-oriented Dominicans and Franciscans (sometimes bishops) - they were not in the habit of writing biographical or slice-of-life stuff.

A word about availability in English: the general public has little use for these raw documents so big publishers are not interested in paying for their translation and publishing. Medieval academics don't generally need them in English as they have been published in Latin and often in French and Italian. If you could read French it would open a very, very large world of resources.

However, there are a few things available. There are a lot of variations on inquisitors' manuals from the 13-14th centuries, but the two touchstones are Bernard Gui (c1262-1331) and Nicholas Eymerich (c1316-1399).

Gui's manual Practica inquisitionis heretice pravitatis has been translated recently by Janet Shirley The Inquisitor's Guide: A Medieval Manual on Heretics.

As far as I know Eymerich's massive Directorium inquisitorum has not yet been translated fully into English, but you can find pieces translated across numerous collections.

You can also find English versions of the late 15th c Malleus malificarum ('Hammer of the witches') around but it can't be taken as an inquisitors' manual - despite the pop culture claims for it. It was disowned by the Church, the author Spengler was a vengeful nutcase, and the manual had little influence on future inquisitors, jurists and witch hunters. But it's a fun read.

For statements of witnesses/defendants of the inquisitio heretice pravitatis, you can look at the very expensive Inquisitors and Heretics in Thirteenth-Century Languedoc: Edition and Translation of Toulouse Inquisition Depositions, 1273-1282.

Below are two collections of primary sources in translation that are more affordable and probably of interest to you, they include a wide range of materials. You can find inquisitorial documents in both as well as other materials.

Wakefield and Evans' Heresies of the High Middle Ages and Arnold and Biller's just-published Heresy and Inquisition in France, 1200-1300.

The Spanish were meticulous in notarizing just about everything they did, and certainly during the inquisitions. Here's a couple of interesting first-hand accounts, based on inquisitor interviews with suspected heretics:

Richard L. Kagen and Abigail Dyer, trans. and eds., Inquisitorial Inquiries: Brief Lives of Secret Jews and Other Heretics, second edition (Baltimore: Johns Hopkins University Press, 2011). https://jhupbooks.press.jhu.edu/content/inquisitorial-inquiries

Sara Tilghman Nalle, Mad for God: Bartolomé Sánchez, the Secret Messiah of Cardenete (Charlottesville: University of Virginia Press, 2001). http://www.upress.virginia.edu/title/2045

I have a question for that. Are you asking about the Spanish Inquisition, the Episcopal/Papal Inquisition, or the Inquisition in general?