Introduction to Linear Algebra, Gilbert Strang, 2016 (Wellesley-Cambridge Press) - Classic textbook providing a thorough treatment of vector spaces and subspaces, with strong geometric intuition and applications.
Linear Algebra and Its Applications, David C. Lay, Steven R. Lay, Judi J. McDonald, 2021 (Pearson) - Widely-used textbook that clearly explains subspaces with numerous examples and a focus on practical applications.
Mathematics for Machine Learning, Marc Peter Deisenroth, A. Aldo Faisal, Cheng Soon Ong, 2020 (Cambridge University Press) - Provides a focused introduction to linear algebra concepts, including subspaces, as they relate to machine learning algorithms and data analysis.
18.06SC Linear Algebra, Gilbert Strang, 2011MIT OpenCourseWare (Massachusetts Institute of Technology) - MIT's free online course, featuring lectures and materials that thoroughly cover vector spaces and the properties of subspaces.