In my experience, you can't dictate the use of project management tools to a customer. If your customer likes email, that's what you're going to use.
I've tried Basecamp with limited success. But that's just my clients. Maybe your situation is different.
(Also, Basecamp gets astonishingly cluttered and hard to navigate when you get slightly busy. I have a group of 10 people creating a nonprofit organization from ground zero -- including legal work, website, etc. -- and it's pure shit to try to find stuff in Basecamp. Highly NON-recommended. So beware the curse of success in persuading people to use a tool like Basecamp.)
This means that you need to keep yourself highly organized in order to remain sane. For me, I am a happy IQTELL user. http://www.iqtell.com
But you might find something else that you like.
See, the problem isn't the tool you use. It's you and your brain. Get that right and everything will be fine.
A piece of paper with a list of stuff on it is fine. Right now I have a list of 9 things on a piece of paper. If I'm not working on one of those, I'm off course.
The usual disclaimers: David Allen is God, etc. etc.
But seriously. Keep it simple. I would say get a Moleskine and a pen, but I lost my paper organizer in a cab in Riyadh and that kinda sucked the farts out of dead seagulls. So now it's all in the cloud and in my phone, courtesy of IQTELL.