Messages - need to be able to organise better and be able to flag messages

It is not clear which messages are read / unread. As everything is in grey print the tiny house indicator of read / unread messages needs to be clearer.
It would be really useful to be able to flag messages for attention.
It would be useful to be able to categorise messages for filing into folders .
It is cumbersome to scroll through hundreds of messages to find a particular msg
Would also be useful to see when you look at a message that it has been responded too … really annoying to have to close the message move to sent and check and then come back to the message to respond