What would be the best corporate structure for my small business?

I own a small business in Massachusetts doing Web development. We’re a Yahoo! Small Business Partner and most of our business is building, upgrading or updating Yahoo! Stores. Right now, the business is a sole proprietorship. But as I get older, I’m thinking through my bucket list. I’d like the business to be easy to pass on to my survivors. They can then sell it or continue to operate it as they see fit.

I also had to take on considerable debt to get through the Great Recession and pay to keep a roof over our heads, the phones on, an Internet Connection and all the costs to keep the business open and able to generate future revenues. I’m whittling that debt down, but not fast enough for the banks. I need to shelter the company’s assets so one creditor doesn’t attach my bank account and leave me with no way to earn money to pay the rest. Not a pretty picture, but it is what it is.

What would be the best business structure to meet these goals? Can I do most of the work to form an LLC or S-Corp myself, or must I retain an attorney to do that?