Advice for leading other developers?

I'm a senior software developer at the company I work for. The problem is that until a year ago, I was the only developer. I'm mostly in charge of the projects and tasks that we both work on.

I feel I've got a good grasp on software architecture, project planning, and the company's goals, but I feel I lack in the skills of managing another person and I'm not really sure where to start learning these things.

Currently the thing I'm struggling with is communicating and mentoring in terms of quality.

• On one hand, I want to let them make mistakes and learn on their own like I did. This way their software quality improves over time.
• On the other hand, as I've grown as a developer the company has grown in software quality and I don't want to lower that standard.

The natural compromise here would be to do regular code reviews, but it feels like I'm having to constantly criticize a lot of things (code readability, consistently, and even null reference exceptions) which feels bad for both of us, but does improve quality.

Does anyone have any advice for this kind of situation or in general? I'm open to articles/videos on such topics as well.