Sharon,
First of all, a warm welcome back to the forum! If you're flying economy, then airport lounge access is not normally included for free, but you can usually pay for it. Tiger Airways is a budget airline so it's doubtful it even has its own lounge, let alone access to economy passengers.
A way of getting "free" airport lounge access that people don't often know about is applying for a Diners Club card, which offers access to hundreds of lounges worldwide. I am not sure if you would need one both or could get into a lounge with just the one joint card. You'd have to look into it to confirm. Regardless, being a holder of the card - which costs a fee to join (it shouldn't be more than $100) - gives you a year of free lounge access and would let you use these lounges at Changi:
Airport Lounge Details | Diners Club International
This benefit certainly applies to US and UK Diners Club members - probably Aussies too, but you'd have to do your research.
Otherwise, the great thing about Changi is it's such a huge, moder, clean and interesting airport. There are comfy seats, bars, laptop area, and even a live jazz band playing when I was last there! It's the best airport I think I've had the pleasure to lounge around in. So even though 11 hours is a long time, even if you don't get lounge access it would be a more comfortable 11 hours than pretty much any other airport worldwide. Bear that in mind!
Have a great trip, and see you on the forums again soon
Steve