Welcome to Community! QuickBooks Online has everything you need to work from wherever you like at any time. I can see how you'd benefit from being able to have an estimate automatically converted to an invoice once your customer accepts it. I'll be happy to provide more information for this, so you're goals are accomplished successfully!
After sending an estimate to your customer, they'll either accept or decline for which you'll manually update the status in your account. The next step is for you to convert the estimate to an invoice so you can send the bill to your customer. Here's a helpful article to guide you through the process of creating and sending estimates in QuickBooks Online.
Please feel free to reach back out with any other questions. We'd be glad to assist!