I was in this boat for 8 years or so before starting a company and hiring a second developer. I lucked out and got a highly research driven one to learn from, and I gotta say I've learned a ton in 2 years. Even if it's harder in some ways than being solo, I think it's been worth it to have that pressure to improve code and processes. I was kind of coasting before if I'm honest, even though I felt like I was really good at my job.