What are the nearest immigration offices for visa extensions in Sukhumvit, Bangkok?

There is no "closest immigration office" as you must go to the immigration office that corresponds to the province you live in, even if there is a closer one. So if you're staying in Bangkok you would need to go to Bangkok immigration.

You didn't tell is what type of extension you want or what visa you're on now so we can't tell you where to go. It's best to give full information when asking a question if you want an accurate answer.

If you arrived with a visa you purchased from a Thai embassy then you go to Chaeng Watthana for an extension. If you entered Thailand visa exempt without a visa then you would go to IT Square Laksi office.

Since you are renting a condo, I assume you are extending a one year visa. If that is the case, you would go to Chaeng Wattana immigration.

If instead, you are extending a visa exempt, you would go to IT Square in Lak Si (third floor).

If you are on an actual visa you bought before entering Thailand you go to the Chaeng Wattana immigration office, but if you received a visa exempt 60 day entry then you go to IT Square Mall on the third floor at the Lak Si office. Those are your only options.

IT square laksi