Folding Bike

Hi everyone. HELP. Due to a few recent health problems,why wife and I have been told by the doctors that gentle cycling would be good for us. We have been to many shops to look at folding bikes we can pop in the car boot or take with us when we go off in the caravan. We are now confused as we have seen so many and always told the good points. Are there things we should look out for when buying the bikes and can anyone recommend any particular make. Thanks. Colin & Sue.