You could look to the Witch class. Higher level spells than the Bard, Better DCs, and Slumber hex.
Not to mention Elf has racial for INT classes so your point buy will be better off as a witch than a bard.
Being up to level 10 you can get the Speak in Dreams major Hex.
You would have 5th level spells Like Overland Flight, Sleepwalking Suggestion, Reincarnate, Symbol of Sleep.
With the Right Patrons, you can get dream as a spell.
Did. But my GM doesn't allow non-core classes as many of them are like... really broken
Laughs.
The core has some broken things in it too. If not MORE than others. Crafting feats, Leadership, Wizards, Druids, and Clerics....
But I would then look to Wizard as you can still cast deep slumber, dream, symbol of sleep, and many other enchantment spells. Bard is a great class but if your wanting to be a CASTER then take a class with better Save DCs and a focus on casting.
I thank you but I'm really set on the Sandman and was only looking for advice on traits, feats and options
You know Fascinate can not be used in combat? Thus the Slumber songs will not be useful IN combat.
Any potential threat, such as a hostile creature approaching, allows the fascinated creature a new saving throw against the fascinating effect. Any obvious threat, such as someone drawing a weapon, casting a spell, or aiming a ranged weapon at the fascinated creature, automatically breaks the effect. A fascinated creature’s ally may shake it free of the spell as a standard action.
The Distraction of a nearby combat or other dangers prevents the ability from working.
Anything is fine for me as long it make the character more useful to the party
That's a pretty broad field. To discern what might be useful to the party, we would first need to know what the party even is. For example, if there's already a witch in the party, then I'd suggest you rethink your plan as they're way better at making people fall asleep than bards.
Might consider eventually purchasing an Apple of Eternal Slumber and/or Naga-Scale Bindi (Dark) when you can afford it. Some of the ioun stones might also fit the theme.
I personally would consider Daze and Confusion effects to be within the same theme as sleep. I think almost all of those are enchantment spells. so Spell Focus Enchantment (and Greater) and Dazing metamagic.
Maybe Moonlight Summons. But it probably isn't worth it.
Coaxing Spell has some interesting effects.
Perhaps a Kitsune Sorcerer with the Dreamspun bloodline or Visionary Wildblooded bloodline.
Kitsune Magic grants +1 to the DC of Enchantment spells.
Magical Tail feats can add many additional spells as spell like abilities 2/day. Recharge Innate Magic.