Being too busy is becoming a problem?

I run a solo Shopify ecommerce and branding studio, and I'm currently booked out 2-3 months ahead. I'm very grateful for this, but it's sort of becoming a problem. Time is money and potential clients don't necessarily want to wait that long and they'd rather find someone else who can get them up and running sooner. Totally understandable, but I don't want to get stuck in the feast and famine cycle myself. What can I do about this? I've thought about group mentorship I could offer to anyone at anytime, digital products/passive income streams, etc. Is it just marketing myself better so clients are more prepared to wait?