all convertible bonds

I have about $1500 dollars in I bonds. How do I know what the return is on them in about 20 years. What else should I invest in. I am a single 42 yr old RN with my kids on there own.
I have a 403B thru my employer with about $40,000 dollars in it and I make about $60, 000 a year. I contribute $300 a month to a credit union savings account, and I am not sure what the balance is on that, probably not more than $1200. I would like to make some investments somewhere, but not sure where to go from here. My home is paid for. It is a dump, but it is mine.

convertible bonds