Because most of what you talk about seems to be related to improving your damage output and combat, my impression is your primary focus is survivability, damage output and combat. I will answer in that light.
Defense. Guidance is an extremely useful cantrip, strong enough to create complaints that it warps how the game is being plaid, but normally you do not make that many skill checks in combat. Even if you had a grappler on the team, you still do not want to sacrifice your action in combat to cast it, when you could be doing full attacks to hopefully score a critical. You also probably want to reserve your concentration for hex. Spare the dying likewise is solid, and is more useful in combat, but it also costs an action. Hopefully you have a cleric with you who can cast healing word as a bonus action instead, which will put the character not only to stable, but back in action. On the other hand, especially if you wear heavy armor and have a high AC, every point to AC counts, it is always on and does not consume your actions or concentration.
Magic Greataxe. For a melee combat character little else is going to be as important as a magic weapon. In a higher level campaign many of your opponents have resistance to non-magical damage (were-creatures may even be immune, but also demons, devils, greater undead and so on). A magic weapon does full damage nearly all of the time, and a +1 one is something few DMs have an issue with granting. That is such a big improvement over half damage that little can measure up to it. If you can choose, a greataxe of warning might be even better, intiative and no surprise for the whole team is very strong. Likewise, if you can get your DM to give you a rare item, a flame tongue greataxe is your best weapon option for damage -- unfortunately, as far as I know there is no uncommon or rare weapon that improves your critical range.
If you have free choice, going by sane magic item prices, which is inofficialy pricing items based on their power, for uncommon you could also try other uncommon items are overpowered for their rarity, for example winged boots or a broom of flying (which might fit thematically into Ravenloft but they would not be a great fit for a melee build), or a helm of telephaty.
For rare, if the DM allows it Cloak of Displacement, giving disadvantage to nearly all attacks against you, or Helm of Teleportation are powerful choices that work with your build. Necklace of Prayer Beads might be even more powerful with the right rolls, but if I were the DM to grant it, I would pick one with low-impact beads. Few DMs would have an issue with granting a +1 Armor, but I would probably take the flame tongue over it.