This has come up a lot lately. You can serch for a more detailed response because at least i have already answered this a couple more times.
For reliable results only sulphites are really the method. Others, less reliable are
Filtration
Fortification (but over 18-19% to make sure it wont referment)
Cold crashing and fining agents and racking. But this is not really reliable.
Ferment until the yeast tap out because they cant keep fermenting (they reach their abv tolerance). Some people have done this, even myself with different results. Sometimes its ok, but if you change the bottles to higher temperatures or dilute the mead after the fermentation, it can cause bottle bombs.
Again all of this is not safe if you plan to backsweeten. Sulphites are found in most foods, so unless you really are allergic i suggest you use them or stick to drier meads. I understand not wanting to use chemicals but in the end if you want sweet meads...