There are a few direction we can go towards in terms of resurrection. Either rules as written, something more like critical role or something like in Aerois/Court of Swords. This will be subject to a vote during session 0:
Critical Role adaptation:
Coming back from the dead is a difficult task that demands a lot of resources and a deep connection with the person you wish to resurrect. The resurrection rituals require expensive material components that are difficult to find. People able to cast these spells are even more rare.
Ritual
The ritual requires the soul of the dead creature to be willing and you to sacrifice some material things to be able to call out to the fallen. This can be paid either in crystal or a magic item of equivalent or higher value (which is consumed by the ritual).
If you wish to participate in the ritual, you must show a meaningful gesture towards the fallen. This can be a moving speech, a call-back to something you have done together, a call to something that still needs to be done, presenting an item of sentimental value as an offering or calling directly to higher powers.
The DM will then ask you to roll a certain skill check. This will reduce the resurrection DC by 2 if it’s a success. The DC to succeed on the skill check depends on the gesture (calling your god buddies “cunts” because they let their warrior fall is a difficult check, having tears well up when looking at the teddy bear of the fallen character’s brother who is now imprisoned in the Evil Guy’s dungeon and calling out to get back here to help the party save the brother is an easy check.)
Resurrection DC
The base DC for the resurrection starts at 10 for everybody. For each consecutive deaths, the DC is increased by 2. When the moment comes, the DM rolls a d20. If the roll is equal or higher than the resurrection DC, the player character is revived, else the ritual fails and death finally can claim its prize
Aerois/Court of Swords:
Coming back from the dead is harrowing for the soul. You are imparted a part of someone’s soul when they bring you back. You can be resurrected ONCE by the same caster using the rules as written in the Player’s Handbook.