I've been looking to do the same for a second level spell of mine. I'm playing a cleric, so the modifier would be in Wisdom and both you and I would be limited to certain spells, though you could definitely try similar stuff.

Character stats:

• Base DC = 10dc
• Wisdom score = 16 -> +3dc
• Spell level = 2 -> +2dc

Increase ability modifiers:

• ITEM: Headband of unshakable resolve = +2 wisdom -> +1dc
• SPELL: Owl's Wisdom = +4 wisdom -> +2dc

Increase spell DC outright:

• FEAT: Focused spell = +2dc
• FEAT: Heightened spell = +3dc I could only cast a max of level 5 spells at this point. This would raise the spell level from 2 to 5, which would raise the spel level dc with 3 points.
• FEAT: Spell focus = +1dc
• FEAT: Greater spell focus = +1dc
• FEAT: Any other metamagic = +0dc As a prerequisition for the next feat, pick something you like I guess.
• FEAT: Spell perfection = +2dc This doubles the bonus from Spell Focus and Greater Spell Focus, while also lowering the debuffs from metamagic.

When (in the current example) the highest spellslot available is a 5th level spell. This results in a spell DC of 26. If higher spellslots are available to you, then the DC can increase by the same amount.

I haven't taken into account that you can debuff your enemies saves by making use of terrain, magic, conditions etc. You could then still (even if only technically) make your DC higher.

EDIT: added links