I would suggest creating an index on _eType and _oType only. This is the simplest solution.
create index feeder_eTypeoType on feeder(_eType, _oType)
With that index in place, the execution pipeline should be an index scan (feeder_eTypeoType), followed by a fetch, followed by a sort. That means the index helps with the selection, but not with the sorting.
Does that deliver acceptable performance?