These are just common gamemodes that work pretty well. Compensation: Works with to3/to4. When a player dies, their maximum health is spread across their remaining teamates. Therefore a solo player in to3 would have 30 hearts max. Arrows also are crafted into 16 instead of 4 (compensation arrows), and as your max. health increases, gapples heal more. (heads would need to be off) Infinite Enchanter: You start with 10000 levels :) Go to Hell: After a certain period of time (eg. 45 minutes) all players have to be in the nether. If not, they will take 1 heart every 30 seconds. Absorptionless: No Absorption. Makes bows a preferable form of attack and prevents excessive chugging. Blood Cycle: Every 5 minutes (starting 10 minutes in maybe?) an ore will be selected. When mining this ore you will take 1/2 a heart Enchantless: Enchanting tables are uncraftable. Enchanted books however, can be obtained. Vengeful Spirits: Upon death, a ghast spawns which you need to kill to get the head.
These are just suggestions. If you search these up on reddit you can probably find them easily :)