If you are the only CSM at your startup chances are your startup is in a seed or series A round. This coincides with a lack of resources directed towards Customer Success but more towards sales and engineering. Although I love Customer Success, I think this is the right thing to do.
That being said if your customers are churning at the same rate that you are bringing in customers well then its time to re evaluate some things.
At the minimum your startup needs a way to track customer health. A good CSM needs to understand if the customer is using the software, engaging in advanced ways, and touching with different parts of your organization. A CSM also needs to be able to write down the status of that customer so they can keep tabs.
I tried doing this for two months in Excel and I found myself fumbling around constantly. It was time to get a CSM software.
Let me tell you… it was hard to find something cheap.
The best CS software out there is Gainsight and Totango. The minimum investement in these tools is around 30k. My budget was max 12k a year!
You will be surpised with the amount of CS software available out there. Keep looking and you will find the right fit. I understand you might have A LOT of things going on with customers and internal objectives but give yourself 1 hour a day to keep looking.
After about a month and a half I was finally able to find the right fit at 15k a year. This software has done great things for my process and has improved our churn rate from 70% to 86%.