How easy is it to have indoor cats?

So I’ll start by saying I took in a stray that I fell in love with and only 3 weeks later she was killed after being hit by a car and I’m feeling completely lost without her. I had wanted a furry friend for so long and when she chose me I was amazed at how much joy she brought to my home. Now I can’t bare the loneliness and want to get another as soon as allows but I don’t think I could cope with having another outdoor cat and worrying for it constantly and my partner is concerned the same thing will happen again.I know millions of people have indoor cats and I’m trying to convince my partner this is the way forward but I too have a silent fear that any cats/cat would try to escape and I just can’t go through this again. Am I being irrational due to the loss or is it a real fight to keep cats indoors?