My Finnish grandmother tells me I sound 'too polite'—how do I make my spoken Finnish more casual?

I’m a heritage learner and I’ve mostly learned through textbooks, so I end up sounding like a formal document when I talk to my family. They keep using contractions and colloquialisms that I never see in my 'Opetellaan suomea' books. Are there any specific resources for learning 'puhekieli' without completely abandoning the standard Finnish I’ve worked so hard on?