hi. i agree with ash. my dd was born in the summer so i just swaddled her with light sheet on the warmer days and a cellular blanket on the cooler days. she did however prefer a sleeping bag cos she liked to wiggle about. they are fab and you can get different toggs for different times of year. as long as you have a babygrow to cover her arms then a sleeping bag should be enough. as long as you have layers which can be added or removed depending on the weather thats fine.
my dd is now 2 and used slepping bags and all in one suits until recently and on the colder nights she would wear the all in one sleep suits over her pjs (the fluffy wolly ones) she is now in a proper bed so has a duvet.
when baby is here s/he will let you know if s/he is too hot or cold and you will soon get the hang of it xxx