Really strange wobble!

Hey guys, I am experiencing a seemingly unexplainable wobble. It’s felt through the steering wheel that shakes. This is also felt by the passenger so not just through the steering wheel. The wobble appears when I travel between 50 and 70mph, only when there is more than myself in the car. If I accelerate the wobble lessens and if I ease of it worsens until the speed reduces below 50ish. (Lower revs at speed more wobble) I have checked tracking, wheel bearings,wheel balance and general look over the suspension with no luck. Any ideas?

1.6 Chevrolet lacetti estate 2006

(Basic mechanic training so go easy on me)