Vs DDD: try Flamethrower, it'll really help your neutral game. It outspaces DDD's Ftilt and you can Flame Cancel it. In that matchup, I Flamethrower tons. It helps mitigate the loss of outgoing damage due to inferior range, and again, I think it really help's Bowser's neutral game. Not just against DDD, but especially against DDD. You're gonna hit him with it a lot because he's so big and his jump is so slow. He's going to have a hard time punishing you because his aerial control is very very weak, since he can't get at you from the ground, he'd be forced to come from the air. At which point you can stop breathing fire. Careful here though, they might start going airborne to bait you into stopping, and then try punishing you out of that. Faster characters will go for that. I usually UpB to a ledge ASAP (broken tactic in general, lol).
Vs Wario: Yeah, Wario does well vs Bowser. I have experience on both sides of the matchup, though more from Bowser's perspective, as there are no local Bowser players near me. With 2.5, Wario's Bite really helps him get in. The fact that he can DI during it is completely gamechanging, and Bowser is the easiest target out there. Wario can DI well out of Bowser's combos (he can't even really hit him out of Uthrow most of the time) and spaced Bairs will really keep Bowser out well. Bowser's Fair out-prioritizes all of Wario's everything, though. He can DI out of the flames easily and really just stay on top of Bowser a lot better than Bowser can stay on top of him. Dthrow is your best throw vs Wario since you really don't have follow-ups on the guy, and Idk, I don't really have a solid strategy for Warop outside of the basic Bowser stuff: UpB, Fair, UpB, Fair, UpB, be careful, UpB, knuckle, UpB... I'd give the matchup a 4/6, at least based on my experience.
My 2 cents on the Fox MU: Fox wins it. The ledge attack is really only super powerful for edgeguarding. Aside from that, using it when Fox is grounded will usually result in Fox shielding the ledge attack and USmashing you out of it. Or really, whatever he wants. Drill OOS to shine, etc, you know what Fox does.