Hey girlies
I never bothered with a sensor mat and I won't this time either. The 2 people I know who had them hated them as they went off unnecessarily all the time and caused too much stress! Holly was in our room til 5 months then went in hers and still til this day I'll pop in a couple of times a night to check she's alright! When she was little she napped downstairs then started her night time sleep downstairs and we took her up with us when we went to bed, so she was never far from us. Holly hated her Moses and so slept in her pram carrycot til around 12 weeks then we moved her cot into our room til 5 months and she napped downstairs for her swing.
With regards to baby sleeping in the dark, my advice would be to not make their room pitch black and silent, otherwise they'll need it that way to sleep which can cause problems when out and about, staying away from hme and at nursery and stuff when they have to sleep in noisy/light places. My friend had her baby sleep only upstairs in her cot with the blackout blind on in silence but she wishes she didn't as she had real problems with her lo not napping in the pushchair when out and so she had to come home for nap times all the time. Holly sleeps anywhere and everywhere through any amount of noise and light and I'm really glad she does, makes life so much easier!
Also I've never heard that about mobiles and stuff! The fisher price seahorse was a lifesaver when holly was little as was her mobile, but she was never bothered about her light show thing. She still goes to sleep with the music on her monitor now. She slept through 11-7 from 10 weeks then 8-8 from around 6 months. Now she does 8.30-9.30 or so, so I was blessed with a good sleeper!the first 6 weeks though she had day and night muddled and was awake all night and asleep all day!!