Eligibility for SSDI is based on work credits, or if your onset of SSDI disability occurred before age 22, you might qualify on one of your parents work records.

Usually SS checks your eligibility for both programs when you first apply. Many states also give additional funds to SSI beneficiaries. In CA where I live, the state matches your monthly SSI check.

Any additional info you'd be willing to impart might be helpful, if you're uncomfortable doing it publicly, you can pm it later on if you'd prefer.

What age did you claim as your onset of disability for your SSI application?

How old were you when you applied for SSI?

How long have you been receiving SSI benefits?

Did you ever work? If yes, how many years? What age did you stop?

Also, if you're struggling financially, receiving SSI will automatically qualify you for some other government programs. SSI is considered a "welfare" program. In some parts of the country Section 8 Housing, or similar programs will give certain categories of people (such as disabled or SSI recipients) a bump to the top of the list.