The only animal I really can't handle living without is a dog. they are family. the only gaps have been due to losses. my big girl is 15 yrs old now & we are treasuring every day. won't be long.
I've always had other animals, but fish tanks were not always possible.
One adopted stray outdoor cat (at a time), consistently. when I have to put one down, another shows up. the last one was about 17 yrs old :-o There's a doghouse/bed under the back porch with heated bed in winter. I feed, pet and pick them up for cuddles. then change my shirt & wash hands, coz I'm allergic now. they keep mice population down.