Essential Spanish Grammar: All The Grammar Really Needed For Speech And Comprehension (Dover Language Guides Essential Grammar)

You could probably avoid grammar exercises with that much input..even just getting a very short primer on grammar and giving it a read through could do the trick; https://www.amazon.com/Essential-Spanish-Grammar-Language-Guides/dp/0486207803 Buy a used copy or see if your library has it. Alternatively, you could get any grammar topic under the sun explained to you in comprehensible Spanish on YouTube if you were so inclined. Grammar exercises are one of many choices and not the only answer.