I think we should create our own kind of necromancy, but one that is intrinsically different to how demonic necromancy works. With angelic necromancy, we enlist the willing souls of dead beings who want to carry on the fight in the name of good. There are a few ways we can go about this without being evil, but like it's mentioned in the previous sentence, all the souls used need to be
willing and give consent.
Firstly, let's talk about zombies. A normal zombie is the result of a necromancer forcing a soul into a body and compelling it to do its bidding until the zombie rots away. Our zombies will instead be the result of a soul being called back into its body to fight once more (key word here is 'called' - they can refuse the call). This not only allows for the dead to be of used, but the purifying energy used to contain them all sanctifies their bodies and prevents them from being turned into zombies afterwards. Unfortunately, this kind of energy is so pure that it literally burns away the zombies flesh (luckily they're dead so they don't feel it, and it's holy fire so it doesn't hurt their souls) and when it's all done burning the zombie will die where it can no longer be raised again. The time until the zombie burns out is anywhere between a few minutes to a few hours, depending on the goodness of the soul.
We can also use angelic necromancy in a different way, and one which parallels Barrsdoom. Barrsoom is infused with the crying souls of the damned, increasing its power and causing terror in all who look upon the axe. What I was thinking is we can make our own axe, and it's a normal axe in all accounts if it needs to be, but it's infused by the power of the souls we freed from undeadification and who willingly joined with the axe in the fight against evil. While Barrsdoom screams and frightens, our axe sings and inspires.
In the previous section I said that I'll explain what we'll make the sword out of and here I'll explain. You see, a sword meant to channel the raw power of an angel in such a refined and powerful way I described would have to be just as pure and good as the angel who wields it. We have four options. One: we simply find/make the sword ourselves and overload it with goodness. This is the simplest solution but finding decent metal to make the sword out of will be a challenge and putting in that much good energy would be draining. Two: we find someone
pure of heart who'll volunteer to give up their life and become our sword. If we can find someone that's pure-hearted convincing them should be easy. Unfortunately, finding such a person would either be very difficult or downright impossible (unless we used angel radar or something....) Three: get a child to become the sword. As the OP says, children are innocent and they're precious - a perfect fit for our sword. The only problem here is the ethical and moral dilemma or turning a child into a weapon. Four: we find a lesser angel who'll be willing to become our sword. There are a few problems with this, namely that we'll have to expend energy to find a lesser angel, the angel might not take kindly to becoming a sword (consentconsentconsent), and simply having a will that powerful that's not our own might conflict with the sword's use.