In my experience the best books to teach yourself Sanskrit are "Introduction to Sanskrit", Books one and two, by Thomas Egenes.

https://www.amazon.com/Introduction-Sanskrit-Part-Thomas-Egenes/dp/8120838149/ref=sr_1_1?keywords=thomas+egenes&qid=1571416759&s =books&sr=1-1

https://www.amazon.com/Introduction-Sanskrit-Part-Thomas-Egenes/dp/8120816935/ref=sr_1_4?keywords=thomas+egenes&qid=1571416759&s =books&sr=1-4

You will also eventually need a Sanskrit dictionary. Try to get as nice of one as you can. You can at times find them pretty inexpensively, but know that the cheap ones will have ridiculously thin pages and the printing can be pretty sloppy.

These flash cards are very helpful for learning Devanagari, and the CD very helpful for correctly pronouncing the sounds:

https://www.amazon.com/Sanskrit-Flash-Cards-Nicolai-Bachman/dp/188372502X/ref=sr_1_3?keywords=Nicolai+Bachman&qid=1571416882 &s=books&sr=1-3

If you feel something more formal might help, these people have a wonderful home Sanskrit course:

https://www.americansanskrit.com/study-at-home-1