Kylie Jenner says she wants to broaden her horizons ... and, by horizons, we mean her already huge boobs!

The reality star appeared on an episode of "Better Half with Stas & Vic" -- hosted by her longtime pals Stassie Karanikolaou and Victoria Villarroel -- published Thursday ... and they jumped into a convo about Kylie's breasts.

Their talk starts with comments about Kylie starting a viral trend when she revealed her plastic surgery numbers on social media ... before Kylie says her 445cc's just aren't enough for her.

That's right, Kylie's a size queen ... Stassie and Vic note she's got a thing for "big t**s" -- adding this doesn't come as a shock to them because she's been saying the same thing for about a year now.

Kylie jokes she wants her boobs to enter a room long before she does ... so don't be surprised if she gets an almost comically large set in the near future.

Of course, Kylie's in a relationship with Timothée Chalamet ... who we imagine won't mind if she decides to go bigger.

Apparently, size does matter!