The Summa Theologiae can be found in a Latin-English in sixty volumes in the Blackfriars edition (Eyre & Spotiswoode, 1963-75).
Aquinas’ philosophy of mind is discussed thoroughly in Bernard Lonergan’s Verbum: Word and Idea in Aquinas (Notre Dame, 1967).
The following are very good introductions:
Copleston, F. (1955). Aquinas. London: Penguin Books.
Kenny, A. (1980). Aquinas. Oxford: OUP.
Turner, D. (2013). Thomas Aquinas. A Portrait. New Haven/London: Yale University Press.