HI, Alex.
While you can wear a bikini or one-piece, that's best if you're transitioning. (Otherwise, you can get some nasty harassment.)
You could wear things and cover up - that would limit harassment, probably.
But the "easiest" solution might be a rashguard, which generally resembles a T-shirt, but is meant to protect the skin.
I think one reason some of us transition even if only semi-passable is because of that "in between" level's difficulty. You don't seem right as "man" or "woman". (Mostly talking perception - this is all the external concerns, not your feeling about you, internal perception; it's how others see you.)
Carlin put it well: "Think of the average person. Think how DUMB they are. Now realize - half the population is DUMBER than that!"
Most people want to pigeon-hole you into a box. It's easier to be pigeon-holed into "ugly woman" than to be "freak," "shemale," "queer" (used in the traditional sense), or even "fat male slob with tits."
So, consider how you can both protect the girls (like a formed suit or top) and enjoy the outdoors (rashguard over the top, maybe a loose T-shirt over that; and may be hot and sweaty! Remember to use some underarm antiperspirant under the breasts, around the crease!)
And be aware, you'll still "show" at certain angles, and look "funny" with a goatee or beard. ;-)