Start with a shared address rather than software. Something like help or support at your domain, configured so it reaches whoever handles it. This costs nothing beyond what you already pay for email and it produces two benefits immediately: customers have a route that does not depend on knowing an individual, and the conversation history stays with the business rather than inside one mailbox.
Response speed matters more than response quality at this stage, within reason. A quick acknowledgement that you have seen the message and will have an answer by a stated time outperforms a thorough reply two days later, because the anxiety a customer feels is about being ignored rather than about the answer itself. Set an expectation you can actually meet and meet it consistently.
Write down the answers you give repeatedly. The fourth time you type the same explanation, save it. That collection becomes your templates, and later becomes the basis of a help page that answers the question before anybody has to ask. Support volume is one of the few metrics where a rising number is a signal to change the product or the copy rather than to hire.
Move to dedicated support software when three things are true: more than one person answers, you are losing track of what is outstanding, and you need to know how many of a particular question you are getting. Before that, a shared inbox with a discipline about marking things done covers it.
Track two numbers even informally, because they answer different questions. How long it takes you to respond first, which is what customers actually judge you on, and how many messages it takes to resolve something, which tells you whether your answers are landing. A rising resolution count usually means your first reply is incomplete rather than that questions are getting harder. Both can be estimated from your inbox without any software, and knowing them makes it obvious when the shared address has stopped being sufficient.
Set an automatic acknowledgement that states when somebody will hear back, since the anxiety is about being ignored rather than about the wait. A message confirming receipt and naming a realistic response time converts silence into a known interval, and it costs one setting. Make the stated time one you can meet during a busy week rather than a calm one.