You can upgrade health and attack power but grinding won’t ever help that. Health you get from getting 4 Prayer Beads and those are drops from mini-bosses or maybe key item pickups in the world, they can’t be grinded for. Attack Power upgrade items are only recieved when beating a boss.
Edit: you probably can grind for prosthetic upgrades but those will still probably be locked behind area progression since they need specific materials, not only money. There are skill points, but I don’t think any of them do anything for damage, just unlock new abilities for combat. So obviously, that can help and you can grind for those, but I don’t that is going to stop you from needing to get better.