You don't need a DPO. I work with healthcare businesses and some of them don't even need a DPO.

You only need a DPO if you are a public authority, if you do large scale processing or large scale processing of sensitive data (ambiguous in the GDPR).

If you collect some data, all you need is a privacy policy outlining such, stating what you collect in general and that your legal basis for doing so is to provide the user a service and to monitor for app crashes / bugs - both within your legitimate interests.

Many people have interpreted GDPR to be stricter than it is. In fact, those who have to do the most work are those that cause incredible damage to individuals when they lose data - especially those that have had recent, massive data breaches e.g Equifax.