I make my living teaching first aid and pre-hospital care. Lots of people ask us for advanced courses, but unless they have already got the basic skills at a high standard they miss a lot from the more advanced courses. There for for those people with little or no knowledge or skills in the first aid field I would suggest a good starting point would be:
Emergence First Aid at Work (1 day) or First Aid at Work (a further 2 days),
Emergency Paediatric First Aid (1 Day) / Paediatric First (1 Day).
Some of the companies offer a combined First Aid at Work & Paediatric First Aid Course, usually running over 4 days, but it gives you the best of both courses.
Another good option would be the Outdoor First Aid Course (2 Days), this teaches the basic skills, but with the idea that help is further away.
All the above courses are available with a RQF certificate, so they are nationally recognised and should cost around the £60 - £75 / day mark at today's prices (depending on location too). I honestly could not tell you how many different companies teach these courses, but it is definitely in the hundreds.
After that you have the option of bolt-on courses, such as the epi-pen for anaphylaxis or more advanced fractures. Some of these will have nationally recognised certificates and some will have a certificate just from the trainer. Don't discount training purely because it does
not have a nationally recognised certificate, there are a lot of independent trainers out there delivering excellent courses.