I don't think it's that much of a death sentence to spend HP for Metamagic options. In the 2014 PHB, all the Metamagic options are 1-3 SP. In the last playtest featuring the Sorcerer (UA7), the Metamagic options were either 1 or 2 SP.
Taking into consideration my suggestions,
A) Being a CON-based caster means Sorcerers should cave a higher Constitution modifier, and therefore more HP
B) If that's not enough, raising the hit die to a d8 should give them even more HP
C) If that's still not enough, maybe capping the amount of HP used to 1/level/day or so would help.
Spending 1, 2, or 3 HP to perform a Metamagic act isn't horrible. Doing some back-of-the-napkin math, a level 5 Sorcerer with a 16 CON (+3 modifier), taking the average HP at each level (and taking a feat at 4th just to keep the math simple) would have 37 HP with a d6 HD (or 43 HP with a d8 HD). Burning up to 5 HP/day for Metamagic isn't Metatragic*. Do people even carry Healing Potions with them anymore? It seems like many people are going the BG3 route by making it a Bonus Action to chug a potion, and an Action only when administering a potion to someone else.
*please disregard my use of the term Metatragic. I didn't get enough sleep last night and am not firing on all cylinders.