The standard adult learner's text used in Britain is "Reading Latin", by Peter Jones and Keith Sidwell. This is in two volumes designed to be used side by side:
Reading Latin: Grammar and Exercises
and
Reading Latin: Text and Vocabulary
There's also a separate volume for people learning independently rather than being taught:
An Independent Study Guide to Reading Latin
There are the books I used when I learnt Latin with the Open University, and I thoroughly recommend them. They are written specifically for adult learners.
All are available as ebooks but I'd honestly recommend the paper versions; they're far easier to use for this kind of thing!
There's an equivalent set of books for ancient Greek, which I also studied with the OU. It's equally good.