TrueBagelMan
Explorer
Have you operated homebrew on DnD Beyond? You need to copy subclasses that are similar to figure how the homebrew maker functions. Without that it’s a nightmare to operate.Why do you need to base it of something? AC 13 (for rocky thick skin) + Con modifier seems to be an ok rule on its own. For the draconic sorcerer it is Dex, which seems to suggest tot you that a Draconic Sorc might need more MAD than your Stone sorc for the same result, still, with the Dex also your reflex save goes up so it is a draw.
And Stone Sorcerer is not a draw with Draconic Sorcerer. CON saves mean Concentration, CON Saving Throws and HP. With this feature it also means AC. DEX saves are still important, but for a spell caster CON is far more important.