Trying to answer the actual question
I have looked at the V20 necromancy paths. I suppose there are other paths on the splatbooks, but I don't have the time to make a research.
Generally speaking, necromancy paths seems not oriented to combat. I suppose that's for a reason. A Giovanni necromancer is supposed to be subtler than that and not effective on direct action. With the help of the ghosts, he can be always ahead of his opponents, and prevent the confrontation, or address it always in advantage. I would try to use those resources. Prepared vampire is worth two, or however that idiom translates into English. More action-oriented Giovannis go for Potence.
But you were asking about Necromancy paths effective when you are already in the combat situation. I think you pointed out the better choice: the Bone Path. How to use it outside the morgue? Well, as I said before, the anticipation is your advantage, so if you know you are going to enter combat, you can bring the corpses from the morgue (assuming you have enough dots). Also, in combat, people tend to die, so sooner or later you could have a corpse to take control of. Sure, it's not as direct and deadly as launching flames at your enemies, but let face the fact you will never have anything like that.
It's a shame that Giovanni killed all Cappadocian and Lamias because their paths seems far more useful in combats. If you and your Storyteller wish and can build a convincing story in which your character can learn the lost paths of "The Corpse in the Monster", "The Grave Decay", or "The Four Humours" you would get what you are looking for, or at least the closer you can get with Necromancy. But as a Storyteller I would make it very hard and you would end owing a lot of favours. Be warned!
But you should consider...
I play non-combat characters very often. There's something that have proven essential when your security is threatened: Retainers.
Have a bodyguard or two. They can be more suited to combat than your character, and your character can buy time to do some tricks with them. Ideally they would be ghouls, which supernatural powers would make them deadlier in combat. But if you cannot create ghouls, you can hire regular goons. A Giovanni vampire usually has the resources or contacts to do this; if not, the family can sure help. Dominate 3 would be very useful to avoid breaking the Masquerade, but other means can be used.
This way, you can still focus in doing what your character knows well, necromancy, social work, finances, or whatever.