QF F wad indeed a great lounge. Open until 23.00 last night.
Entry without BP wasn't possible, ticket number didn't do it. However, transfer desks seems to be open all day so if you are connecting at SIN and already is airside getting BP can't be a problem.

If you are travelling with kids QF F is relaxed with entry rules. I had mentally prepared Ms. that she might end up in Business lounge, since I was heading for F, and Oneworld entry rules says Plat +1. They turned out to have similar rules as AY in HEL. I guested Ms. and was allowed to bring 5 year old without hesitation.