If you want to keep all the parts currently on it, I'd get another window visor at least. The carbon fiber trunk takes a lot of attention and makes the rest of the rear look empty imo.
There are two OEM sedan spoilers in the US at least btw. The '96-'98 (with a little "leg" in the middle) and the '99-'00 (which looks like a pointier '96-'98 coupe spoiler). Then there's also the SiR type spoilers for overseas sedans, Mugen style spoilers (which I think would look bad on this car), lip spoilers, etc.
With an SiR front lip I think no other rear lip really matches. So if you put a rear lip on you're going to want to change the front lip unless you want the rear top look heavier.
The '99-'00 rear bumper might work, but I think it will look too sharp compared to the stock shaped trunk and inner taillights.
The rear end currently has a very round look to it. Adding a rear lip would be good for the rear, but I don't think it'd work with the front end you currently have. Adding a spoiler would look good with a stock trunk, but not with a carbon fiber one.
There are plenty of other different accessories for the rear of your Civic though.