It's about 6 years since i've been to Singapore but i think you may be underestimating the amount of money you'll need with £350. I found Singapore horrendousley expensive (but wonderful!). We did KL (3 nights), Singapore (3 nights), and Penang (7 nights), and took £1000. We spent all of it and about half of that was in Singapore alone. £16 for a 2 pint jug of beer....and about £8/£10 each for singapore slings. Obviousley depends where you go and we did find cheaper, but only because i was visiting a friend living there and she knew where to go.

Singapore is an incredible place so you'll have a ball!