Sleep sacs are fairly freely available, I know Babysense sells one and you can get them at Woolies.
For me the "secret to sanity" was one of those wall heaters in baby's room.
I dressed baby in a vest and babygrower and placed in cot with a blanket, and then if baby kicks of blanket, it was fine as the room was not hot, it was just comfortable.
I also had the sleep sacs, but I found - for me - they were great for newborns, but once baby got past 3 months I preferred not to use them. I also did not find them as user friendly as they could be.
i.e. baby falls asleep in your arms while feeding and is not in sleep sac, and you want to put baby down in cot, but now to try to get baby into sleep sac will disturb baby.
Wall mounted heaters definitely the winner - we also ran a thread like this last year with the same question, and the heater came up as the choice favourite then.
Maybe this year someone has another idea .....