I will say what I always do - make sure you're wearing the right bra size. It makes a huge difference in multiple areas. I question if you are because I know someone who wears a 30E (and has a 23" waist) and they can look basically flat-chested just by wearing certain clothing. A well-fitting bra can alleviate all kinds of problems !
Picture of the difference the right bra makes
(totally "safe for work", she is completely clothed). And you'll notice she's an HH but her figure is not comically busty. You'll also notice the big difference it makes to wear the right size. And not only is it just what you can see, it's more comfortable too.
Ultimately, it matters what you
want to look like. If you want to look more like a little girl while wearing full-on Lolita clothing (which many do and I'm not disparaging that - it's up to the person what they want to look like) - there are certainly things you can do (minimising bras, a bit of compression, cuts of the tops/dresses that will look "less developed"). If you don't want to, that's also your choice. It depends on why you like Lolita as a fashion and what you want to look like. It's totally up to you.