Hi, I retired last year and bought an Alto recorder. I'd always planned to learn to play after being forced to play desant, a bit, at school. I have progressed fairly well on my own (I think) and bought a Sopranino last Xmas for fun. I note that the Bass uses similar fingering as both these. As I play purely for my own pleaseure, can I use a Bass to play the same tunes as I play on the Alto and Sopranino?

You can play the same tunes with the same fingering on any recorder. The result on the alto will be an octave below that on the sopranino, and the result on the bass will be two octaves below that on the sopranino. (The result on the soprano will be a perfect fifth below that on the sopranino, and the result on the tenor will be a perfect twelfth--an octave and a perfect fifth--below that on the sopranino.)