You don't need to use the Ionian boots of Lucidity, as you have three itens with the necessaire cooldown.
You can use Iceborn Gauntlet or Frozen Heart, it's opcional. Both are helpfull for you and the team.
Try to explore the differences and see what you most need in every game.
As a support it's better for you using Frozen Heart, that reduces the attack speed of nearby enemies and offers armor, mana and cooldown.
But if you have to assume an offensive position in game, then Iceborn will be a better choice (and Rabadon as well). Iceborn gives cooldown, armor and AP, dealing with bonus physical damage in your next basic attack, after using an ability.
You can improve your abilities as support using Frozen Heart and Iceborn, excluding the Rabadon from your build.

You can change the seals of Mana Regen to Seals of Armor.
Can replace Gold quintessence by the Quint of Ability Power. In that case, I recommend using Seal of Armor.
As a support it's better staying with the Gold Quint. Between the seals, of armor or mana regen, it's opcional.

as strategy in early game, try too ward the map and stay in bushes, hitting your enemies while your adc is farming.
When attacking the enemy in bushes, dodge his attacks or turn away from him as soon as possible. That way you can drive away your enemies and force them to use their skills, especially the enemy support, spending his mana.Then facilitating the game to your adc and avoiding attacks on him, improving your positions and leading to a team fight victory.
Sona skills have long distance, then try to hit your enemies as far as possible, always beside your adc. Do not try to be too offensive because it is not mid; you have to worry about the safety of your adc and the surrounding area, intercepting jg and other lanes attacks. As being a support stand back, improving the game to the adc, without compromising the lane and teamfights.