What you are looking for is a fixed IP address. Accounts with fixed IP addresses are more expensive than ones without. You have no choice but to use an available ISP if you want to use your personal computer as an FTP server. Talk to your current ISP about upgrading your account to a fixed IP address.
You need to ask yourself if this is what you really want. Your ISP probably already gives provides FTP space on its servers for your account. Why pay the extra money for the privilege of having strangers enter your home via the Internet and generally lower your security? Legitimate users don't care where your files are if they have access to them.
