Hi and welcome to the Forum, and good luck in finding a caravan. Your question wrt what works for others has a really long list of potential replies, as few individuals are the same. Firstly if you plan on taking your granddaughter you will probably want a four berth. We took both our grandchildren out lots of times, virtually every school holiday, and pre school age too, they are now aged 30 and 18 years and we all really enjoyed it. Buying new or pre owned, , budget, single axle or twin axle, your tow cars capability, dogs, where to keep it, fixed bed for two or make up the front lounge bed, private purchase or dealership.
I would recommend sitting down and making a list of your preferences and restrictions. Reading some magazines etc. Then go along to some large dealerships and just go around to look at the layouts and sit in them to think through how you would use it. Practical Caravan magazine has a section that details all of the various layouts on the market. Wander around the two Club websites. Caravan and Motorhome Club, Camping and Caravan Club, lots of technical help sheets, descriptions of all of their sites, details of their events like rallies, overseas trips, temporary holiday sites. , local groups etc.
Cost effective relates to an individual’s own perception of value. Since we started I think that the real cost of caravanning has increased. Certainly since the pandemic and staycations the price of caravans has rocketed both new and pre owned, as has the price of cars. It may well be that as the cost of living increases bite that bubble may burst. If you can use the caravan frequently then it’s cost per diem reduces. The two Clubs have a wide range of sites called Certified Locations, or Certified Sites. These can range from a green field with only a facility for water and waste, to some with facilities that rival larger sites. The Clubs and private site owners again provide a wide range of facilities and price will reflect those facilities as well as time of year. We bought a new van in 2005 and used it all year round, later caravans are all suited for 12 month usage and are extremely comfortable. Ones with solar panels can be used “ off grid” which gives flexibility of sites.
We sold our caravan last summer not because of heath or financial reasons but because of family commitments we weren’t able to use it in other than constrained circumstance, the tow car then went last August. I felt extremely sad as we had enjoyed or caravan touring both solo and with family in Britain and abroad, but it was the right decision.