Minecraft wiki entry for Superflat_survival, associated text: Oak doors as it is easier for zombies to wipe out villagers
Beds as it causes the villager to lose their house which could potentially can make them wander out of village for searching unclaimed beds.
Workstations as villagers need to work at their workstation to resupply their trades, breaking workstation blocks have a chance to transform the villager's profession into unemployed, who cannot be traded with.
Bells as it is required for villager to gossip during mingle behavior for iron golem spawning.