Book about ordination in ecology
I took a class in ordination methods a few months ago and found the following books helpful in better understanding the various techniques:

Multivariate Statistical Methods: A Primer by Brian Manley https://www.crcpress.com/Multivariate-Statistical-Methods-A-Primer-Fourth-Edition/Manly-Alberto/p/book/9781498728966

Correspondence Analysis in Practice by Michael Greenacre (this is somewhat more in-depth for forms of CA) https://www.crcpress.com/Correspondence-Analysis-in-Practice-Third-Edition/Greenacre/p/book/9781498731775

Multivariate Statistics for Wildlife and Ecology Research by McGarigal, Cushman, and Stafford https://www.springer.com/gp/book/9780387988917

Numerical Ecology is really excellent, even if it covers a broad number of topics. I focused on the ordination methods and found it to be very straightforward. Check out the McGarigal et al. book if you are interested in seeing examples of application in ecology.