I coach a lot of entrepreneurs who are trying to find balance and monetize their services without going crazy. You are not alone! There is no set way to bill clients for hours and projects and I've seen this issue come up A lot with over-givers. Especially those consultants who are perfectionists and want to make sure something is right for their end user regardless of how long it takes. While I applaud the quality of work, it is incredibly important to not over-extend yourself and your offerings.
As each client, as you pointed out, is different and requires a different amount of effort and scope per project - a simple hourly rate with your other obligations isn't a perfect fit for you. Don't beat yourself up, it's not about "growing up" or doing it the right way. It's about doing it the way that creates abundance for you and the highest quality work for your clients. If I may offer a hybrid solution that may work out best for you as you seem to not have a per project problem but a "knowing your limits" challenge:
Use an a la cart method of project selection and bill by project with written limits and expectations included as well as a set limit of hours devoted to each project.
For example, a public relations professional I was working with set her press releases with a maximum of two rounds of edits. If more is required, charge for the excess hours at a discounted rate.
Now go a step further. Whether you have a website or not, you can start using a service like acuity scheduling.com to bill and book projects directly onto your calendar and availability so your clients have the freedom to choose when they want you to work on a pre-packaged project during your availability, and can even add discounted hours automatically should they need them.
This level of automation takes the guesswork out of your billing question and saves you from going crazy with overwork and over-extending yourself.
Let me know if this sort of solution would fit in your particular work environment and please call me to discuss further or if you have any questions, going over your packaged pricing and reverse engineering the projects so you aren't over worked is your next step. Sometimes, simple system strategy and knowing your resources can make all the difference!