You don't transcribe blues songs. You get a rough feel for how they go and then go play them. Blues is nothing if not improv. I was the house bass player for an open mic blues night once a week for years. Never saw a sheet of music or a chart.
Now, learn yourself some chord structure. That's where you can lay down some blues. Find some charts of songs you like and study the chords contained therein. Build your bass lines from a combination of your new-found chord structure knowledge and listening to the original recordings.
But really "studying" the blues is kind of like getting a degree in eating pizza. You don't need a degree to eat pizza. Figure out what you like, and then eat it.
If you're gonna be stupid, you gotta be tough. - My Grandmother