I'm probably going to get violently hated/refuted for saying this, but I think a good Y shaped antenna works pretty well. You can buy some expensive indoor concoctions, including the "amplifying" types, but they don't really work that much better than the aforesaid. Amplifying sh*t doesn't work well.
I remember I paid a good £250 for a great rooftop many years ago. Did it make a great deal of difference? No. But it is the standard advice. And it probably is a little better than a Y antenna, in my experience.
Make sure your Y antenna is at least 2-3 metres long, with the Y-split about half way along it's length. Then just keep putting the two Y bits in different positions until it works as best as you can get it to.
Tell me if I'm wrong. But be honest based on your own personal experience. I'm as curious for better information as you are.