Hey! From my experience on softcore, I used cold sorc with equip suited to maximum survivability and quite below average damage, that allowed to make lvl 95-99 with no deaths, unsure whether it would work on hardcore connected with lightning and infinity. I can recommend mentioned stormshield (when using max block, but it did not work good with low hp), also filling inventory with life skillers or small charms was helpful. Thundergod was also mentioned, and for me it worked best when connected with stacked light res (against conviction souls, can be achieved by using ort rune, perf topaz, charms 20 life/11 light res or similar non perf), preferably max light res above 75. Downside - if I remember correctly, thundergod was casting fist of heaven and that was making teleport impossible for a short time.