[1.14.4] What is the best way of saving data on player?

Hi Modders, 

I'm working on a mod where a player starts with 1 heart and every time they die they gain a heart until they have 10 hearts.

But I struggling with how I save the amount a hearts the player has. If I put it in the player data, it will be deleted when the player dies. Same goes for capabilities.

I've tried it with a Hashmap but I know its not the best way of doing thing so I'd like some feedback from you guys. 

Thanks.