I just hope the temperature doesn't drop below freezing.
Literal
Freezing-point [until-まで] getting-cold [even-さえ] [if-not-しなければ] fine [emphasis-ですよ].
氷点下まで冷えさえしなければいいですよ — the さえ...ば pattern means 'if only/as long as.' The negative conditional しなければ + いい means 'it's fine as long as it doesn't.' 氷点下 means 'below freezing.'