OK, shooting for 11 HD, Large, CR 8. Here are comparable oozes:
Arcane Ooze: Str 22, Dex 1, Con 26, Int —, Wis 1, Cha 1
Black Pudding: Str 17, Dex 1, Con 22, Int —, Wis 1, Cha 1
Corrupture: Str 31, Dex 1, Con 29, Int —, Wis 1, Cha 1
Obsidian Ooze: Str 20, Dex 1, Con 20, Int —, Wis 1, Cha 1
Void Ooze: Str 20, Dex 1, Con 26, Int —, Wis 1, Cha 1
We should probably lean toward the high end of the ability scores to warrant its CR as higher than the black pudding.