I kinda know what you mean, especially when I'm on another device and I think "I know I've read that one, urrh!"

What alternative do you think would work? Usually on email applications the unread items are bold. If different colours were used that could be confusing (maybe). Perhaps the title could have an icon next to it to show it is new?

The bold font is well known method and most users know about that. It's too popular method to mark topics as unread. Almost all popular forum platforms use this method.