Hmmmm...in that case things are not looking up for you (at least in terms of getting gold).
Yes, TG and AC could require more miles but at least you earn miles! I think (but have a look on
www.thaiairways.com) with TG you can earn the miles in a 12 month period but you wouldn't have enough trips to get to 50K.
If you don't fly much why are you so keen to get lounge access? You may be better off trying to maximise your mileage.