Welcome!
There's lots of different types of airgun shooting - and some of the target disciplines are very much standing only!
My suggestion would be that before you splash out on any type of gun, get yourself down to a couple of local airgun clubs - in many, you're able to try different guns (in fact, most I've frequented over the years many of the people there are more than happy for you to try their gun). Try clubs that do a mixture of target and plinking for fun ranges, and decide then which you like the most.
Best of Luck!
steve B