Usually if you can get above the inversion layer it's much smoother. Unfortunately in the UK there's often level restrictions that keep you low. It's easy to spot, the air is much dirtier below it and if there's enough moisture you'lll see some little Cu clouds. Note, it's often quite bumpy just near the inversion layer. It may sound nuts but if you have the space, fly lower than it. eg 500' -1,000' below it.
Either fly early or late, midday is the worst time. Greatest thermal activity and windspeed.
How to cope? as stated, don't fight the aeroplane. Keep it rougly on track and on height. Also, keep yourself cool. Drink some water and wear comfortable/breathable clothes. Keep the air circulating too. This is very important for your pax. I'll feel crook as a pax long before I'll feel ordinary as the pilot.
After a while, you really do get used to it and it won't bother you much.
As an aside, I was flying a Shorts 360 around Coventry at lunchtime yesterday. I was doing an LPC. It was hard work keeping it on track/height too. We would have weighed about 8.5 tonne at that time. Still, been in a lot worse conditions.