First you can either buy (requiem gold) a full armor set, a full jewelry set and of course a weapon and/or shield at grocer or use the massive drops you gain on level 50 mobs if you don't have that much cash, stay on white armor or jewelry parts.
Since you have some time to level (requiem lant) to 55, you can reinforce your gear slowly until you are able to raid a boss that can hit you for 2.1k damage at once. 5 armor parts with 5 slots to reinforce 25 possible slots to fill with HP. Fully reinforced with 20 HP xeons you gain 500HP, average will be 400HP. fully reinforced with 30 HP xeons you gain 750HP, average will be 600HP.
8 jewelry parts with 5 slots to reinforce = 40 possible slots to fill with HP. Fully reinforced with 20 HP xeons you gain 800HP, average will be 600HP. Fully reinforced with 30 HP xeons you gain 1200HP, average will be 900HP.
Earrings, Bracelets and Belt have on average 250 HP extra HP and all jewels parts around 16 CON, what is equal to 80 HP. All armor parts give you also at average around 300HP and 20 CON, what is equal to 100 HP.
Your average 20 HP set has now 1.730 HP, your average 30 HP set 2.230HP. All made with simple ordinary xeons in Requiem. Et voila, you can already stand an Earth Shock Crit, if you would be level 1 with no stat growth. For those who weren't unlucky like 90% of the 65+ player base (it seems most are poor and got no drops at all), for sure you can use also supernus reinforced items, which will give you maybe another boost up to 250HP.