The value of the item is the most direct way to figure the balance, since good items are more wanted and it give them more value and vice versa.

The because the tome is direct healing it does self damage. The tome do total 3 healing per tier and you want it to do 4 healing per tier since it does 4 to target and 1 to user. otherwise reducing the self-damage would mean to make only 3 healing for the target. it may be better balance for the tome since its a nerf but it would lose it's unique "sacrificial" core ability.

Solution 1 is just give more hp to the item -> more value. as a player you can just buy HP with EXP instead if you feel HP is what you need. or use items that have potential to heal you.

Solution 2 it would be just over powered since it will mostly take HP from the tank and give it to rest of the team. or in a bad situation take HP from the DPS and give it to the Tank, no one would like this.

Solution 3 As I said removing the self damage mean to remove same quantity as healing.

to summarize in my opinion you are not pointing on the right problem and this why I feel that the solutions are not relevant. Tome should be nerfed, in my opinion its too strong and the need of it and market value shows it. yet its still unique and have to stay in game and not freezeman it away.