It really doesn't get easier, everyone has always got some 'advice' for you. I have learnt to listen to it all, then ignore most of it!!!
What your MIL said about day and night clothes isn't as silly as it sounds though!!!!! I started having day and night clothes at 10 days for LO , so at about 7 we change into night stuff and my LO has slept through the night since. Also I started putting LO into her bedroom for her naps rather than the moses basket in the lounge at about the same time and she slept so much better!!!! Mostly because people couldn't pick LO up or deliberately make noise to wake her! I wasn't offered this advice though, I just discovered it!!!
What your MIL said about day and night clothes isn't as silly as it sounds though!!!!! I started having day and night clothes at 10 days for LO , so at about 7 we change into night stuff and my LO has slept through the night since. Also I started putting LO into her bedroom for her naps rather than the moses basket in the lounge at about the same time and she slept so much better!!!! Mostly because people couldn't pick LO up or deliberately make noise to wake her! I wasn't offered this advice though, I just discovered it!!!