Interesting. In (Brazilian) Portuguese, "isso" and "isso aí" ("this", "this there") is used to confirm or agree with something, so it seems the expression survived the times.
> 'itsso, eh'
Trivia: notice 'isso aí' has an acute accent on í which indicates the syllable is stressed. Doesn't sound much like 'eh' https://translate.google.com/#pt/en/a%C3%AD similar to 'itsso ah-E'.
Esto (isto) = this (at hand's reach)
Eso (isso) = that (close but out of reach)
Aquello (aquilo) = that (far away)
Isto and isso are both "close" but they're still different degrees of closeness. I would still translate 'eso' as 'that'.
EDIT: But I guess you speak Brazilian Portuguese:
https://en.wiktionary.org/wiki/isto#Portuguese
https://en.wiktionary.org/wiki/isso#Portuguese
> isso: (demonstrative, informal, Brazil) this