I used to take DS on holiday as a lone parent from him being 2 years old.
Our 'proper' holidays abroad to resorts were Lanzarote( a few times ) Salou, Calella, Benaldmadena. All quite easy places - as in family orientated, English widely spoken, not too far away.
The first time Ijust booked a last minute (the night before!) trip to Lanzarote. No time to worry about it - we ended up in a nice enough place and had a blast.
One place that we went to just a few years ago - he was about 14 then - was Calella just up the coast from Barcelona. It was nice as quite a small resort, low key. You can get a package trip there very easily. I sort my own hols out - but a flight to Barcelona can be had quite cheaply from many UK airports. Then the train from airport to main train station, local train to resort.
I wouldn't say it was particularly plush -quite a 'value' place but I felt at ease being on holiday there. We didn't do all inclusive as prefer to eat in local restaurants but there will be many hotels which do AI.
Don't worry about being a lone parent with your son. All combinations of families/friends take holidays. People go alone. All is good. As long as you do a bit of research first - look at the map, streetview the resort to get an idea of where you will be. It helps to prepare you for when you arrive.
Does your son learn any languages at school ?