I will recommend few books and lectures on Quantum mechanics and quantum field theory from a mathematical perspective
A. Alekseev lectures on Quantum mechanics and Quantum field theory for mathematicians will give a good introductory taste for quantum theory, as you told you are from a mathematical background. Saurav Chatterjee notes on Introduction to quantum field theory for mathematicans will also be a good one for starting point as well.
Quantum Mechanics for mathematicians by A Leon Takhtajan.
Quantum Theory for mathematicians by Brian C. Hall.
Spectral Theory and Quantum Mechanics by Valter Morretti.
Quantum Field theory for mathematicians by Robert Ticciati.
Towards the mathematics of quantum field theory by Frederic Paugam.
Mathematical Methods in Quantum Mechanics: With Applications to Schrödinger Operators is also mentioned in the answer box as well
The book Foundations of Quantum Theory: From Classical concepts to Operator Algebra by Klaas Landsman is available free on Google books.
Also one book that I should add one is the book, A Combinatorial perspective on Quantum Field theory by Karen Yeats This one is a brief book dicussing the combinatorial inclination of the subject of Quantum Field theory, pdf format is also available, it is ought to be research oriented.
https://www.math.uwaterloo.ca/~kayeats/teaching/co739_w18/A+Combinatorial+Perspective+on+Quantum+F.pdf
Thanks