Here is what we have on the PBE :
Now the main problem is here : by nerfing the self heal, you make Soraka useless because she rely on healing back on her Q to heal on duo lane. I can understand that the free low mana cost healing and movement speed when running from enemy can be a pain for top laner. Top lane Soraka rely entirely on hitting those Q and poke while healing to negate incoming poke since the main top laner roster is melee so range priority can be a nightmare to deal with. Problem is by nerfing her self sustain for top lane, increasing the mana cost and nerfing the movement speed, you basically gut Soraka from support role as well . The current meta is engage and hook support and misspositioning often result in a death sentence. The poke being done by the enemy ADC, you could Q from time to time and soak the harass while keeping your ADC healthy, but if the proposed change goes throught, Soraka won't be a wise choice in any situation and will most likely be replaced with better healer like Nami or Sona since her nerf is basically a buff for duo lane.
So here is my proposition: In the past, the rejuvenation got moved from W to Q. I think it should be reverted and you have to max W to get better healing on Q instead. By doing that, you force Soraka to actually invest in W if she want better healing so it's less appealing in solo lane as you can't heal anyone but the jungle who come from time to time. Maxing Q get lower value since the damage is not as good as right now and she doesn't heal as much either.
She doesn't need much base stat change or W change other than that and I garentee you, she will go back to being support only.