For some years now the Biblioteca apostolica vaticana has been digitizing its many manuscripts and, just in time for Easter, has just made available St Thomas's famous autograph manuscripts Vatican Latin (Vat. Lat.) nos. 9850 and 9851. The former carries portions of Thomas's Summa contra gentiles (snippets from books 1 and 2, and a good bit of book 3), and from his early Scriptum super Boethii de trinitate and Super Isaiam. The latter contains a lengthy section of his Scriptum super III librum sententiarum. The first manuscript (9850) has been especially mutilated over time, with people snatching this or that folio as a souvenir. Indeed, the manuscript you see on the Vatican site is today a bundled heap.
As is well-known there are few people today who can read Thomas's personal handwriting with fluency (Adriano Oliva and Robert Wielockx are two whom I know of; are there more?). On one folio Thomas's beloved secretary, Reginald of Piperno, gives an indication that the same was true even in his and Thomas's day:
It may also be to Reginald that we owe an adorable little doodle of a donkey's head (Gauthier, Somme contre gentiles , p. 19); Thomas's text that ends f. 14vb is: "...unam habere sicut [et] homo et asinus in quantum sunt animalia..." (SCG I.54).
Let the exploring and learning begin. I'll never get to the point where I'll be able to read Thomas's hand easily, but going over the manuscripts does give one the sense of the pace of his thinking, and at times possible directions of this thinking, some of which he thought the better of, and changed outright.