Working up a character for a one shot game

[holywhippet]

I'm building up a battle master fighter (5) / war domain cleric (4) for a one shot game. I've given the character the great weapon master feat since I plan to focus heavily on hitting things with a greatsword. I'm planning to use the ability to trade accuracy for damage in most fights and to offset that I'm thinking of using bless to help offset the accuracy loss. Since I plan to be the the front line a lot I expect to get hit a fair bit so I was thinking the war caster feat would help me avoid losing concentration. However, I've taken fighter as my first level so my constitution saving throw is pretty good - possibly good enough to rarely fail the saving throw. I was thinking instead I should instead get another +2 to CON which will make the saving throw even harder to fail (it's already at 7).

Any thoughts? Alternately any idea what else to take as a feat. The character is a hill dwarf with stats:
STR: 13 (19 since he has gauntlets of ogre power)
DEX: 12
CON: 16
INT: 11
WIS: 18
CHA: 13

The DM is letting us start with magical items so I'm taking adamantium plate, flame tongue great sword, javelin of lightning and a cloak of displacement.