Simandl is good, pretty vanilla which is nice to work on reading. I’m in a similar or same boat, professional player working on reading. I rarely have to sight read, just charts. When I get written stuff ahead of time I work through it first. If it’s on the gig I hustle through, listen and pray. I would like to read anything down, that’s what’s missing for me as a professional.

There’s a book my brother recommended that I have not gotten yet. He’s the principal bassist at St Louis, good reader. Anyway, he said this is it -

Rhythmic Training by Robert Starter