I'll be honest with you, Xyro's ledge thread is good for very few things, but doubles is one of them. Get a partner who's familiar with you, then camp the ledge.
When they walk away, threaten them with missiles and z-air to come back. Off stage is where you shine of course, but make sure your partner knows to keep the other one distracted and leave off-stage battles to you.
Your partner has to know that because of your projectile spam, he has to limit his aerial mobility and stick to ground moves. But in return, he gets cover fire and fewer options to predict from when approaching an opponent. And trust me, when you're on the offense and they can't use aerials/air dodge, it's a blessing.
Samus is a stock tank foremost, and a game changer at best because of her spike. Otherwise, avoid 1v1s, not because Samus can't handle it, but you're best when you have a positive exchange ratio on damage. And what better way to do that than to not take damage at all?
Her best partners are MK/D3/Kirby IMO. But then again, all of those three are sick in doubles already.