I'd go straight paladin - you get your level 5 power bump of extra attack, and continue until AT LEAST level 8. Your level 6 & 7 bumps will be nice,a nd then you want the ASI. There are some good guides on paladins in this forum, so I'm not going to repeat general build suggestions.
Is your group having problems with individual deaths, or just full wipes? My experience is that usually helping the group succeed is the best personal survival as well, so I'm going to make suggestions along that line.
While many say that the best defense is a good offense, D&D is a team game letting those others focus on pure damage may be the better way to go. If you'd rather go heavy offense, go Oath of Vengeance and pick up the Great Weapon Mastery feat at 4th.
But for defending your party, Oath of the Ancients will give you the best defending. At level 7 you'll have an aura that grants Resistance to all magic in addition to your Aura of Protection at 6th. These mean that even if you bunch up, many area of effects won't hurt your party that much with likely saves being made and then Resistance on top.
With such good ability scores, you can afford to take a feat at 4th. Polearm Mastery could both help protect your friends as well as increase your damage output - every attack is a chance to crit and therefore lay on a lot of Divine Smite damage (since those dice are doubled as well). But there are plenty of directions. You could go sword and board and pick up Shield Mastery - if you prone opponents both you and your teammates can finish them off faster. Advantage allows you not only to hit more, but also more crits to double your Divine Smites. Actually, if the Holy Avenger is a sword this might be the best way to go.
I talk about Divine Smite, but many of the other smites have great riders for helping to debuff foes temporarily. Look at them when you don't have another concentration spell up.
I'm partial to Half-Elf for paladins - +2 CHR, +1 to two others, some extra defenses. On the other hand, many like variant humans for a feat.
I'd go for the +2 item - one rare is a better find than two uncommons, and it will retain it's usefulness longer. With the Holy Avenger as a possibility so you don't want a weapon, +2 Full Plate and a shield gives you fantastic AC. You'll have the CON (and soon CHR to saves as well) to keep up concentration so Shield of Faith (bonus action cast) is +2 more AC for a 1st level slot. That would bring your AC up to 24 when you need it.
With all of the aura goodness, I'd put CHR above CON - this way you have great saves and great AC. If half-elf, maybe:
STR 18 (17+1 racial)
DEX 14
CON 16 (15+1 racial)
INT 10
WIS 15
CHR 20 (18 +2 racial)
FEAT: Shield Master
Wasn't sure about the 14 dex and heavy armor, but DEX adds to so much other stuff, plus it will help your Dex saves for single target effects as an extra bonus from Shield Master.
Oh, and pick up +2 STR at 8th to stay on curve. With half-elf giving +2 CHR, it made more sense to max that now, instead of have 19 STR and 19 CHR - same STR mod, but one lower CHR mod.
These build bones gives you a character with fantastic saves at 6th level that you can share with others, great AC, ability to prone foes to both help control the battlefield but also allow you and other melee characters to attack with advantage, Resistance to all magic damage at 7th that you can share - stand near the rogue when he disarms a trap, etc. Very survivable, helps the party survive on top of normal paladin goodness in that regard, and help offense as well as beign able to dish out a good deal.