Do you think a RWS 48 side lever might work for you? If a PCP and the needed accessories are to expensive.
If I understand your dilemma, it has to do with springers not being an option due to difficulty cocking in the prone position.To choose the right rifle for you, the distance you plan to shoot and the money you expect to spend would be considerations. For a PCP you will need a pump at the very least, or you could use CO2. You need to learn the gun because, unless it's regulated, the point of impact shifts a little as pressure drops.Another option might be .17 HMR. I find that is available even when .22 LR is not. Savage puts out a nice line of them and they all seem to have adjustable triggers. They are a bit hotter than a .22 LR but they shoot pretty flat.