I received an email enquiry and I thought I'd share my responses on the blog:
"... I learn languages quickly but it is much easier for me to learn a language if I have a more formal grammatical introduction to the language.
1. Is there a book, either obtainable on-line or in the UK (where I've family and friends) which you could recommend for learning Welsh that way, especially with regular lessons, vocabulary and readings as the grammar is covered?
2. Is there a good and thorough dictionary you would recommend giving Welsh-English equivalents and vice-versa?
3. Finally, I regret to say that I am woefully ignorant of Welsh literature written in the Welsh language. I do own a Welsh translation of Harry Potter but once I've learned the language well enough to read that translation, how can I find out about what there is to read properly in Welsh?"
Re: 1 -
This is interesting as it emphasizes the fact that different people learn in different ways. SSIW (https://www.saysomethingin.com/welsh/course1) is the first option many recommend but this is very much a course about developing speaking conversational skills over grammar, at least as far as I have experienced listening to course 1.
A better option in this case, and a course I can personally recommend, is Catchphrase (http://www.bbc.co.uk/wales/catchphrase/catchphrase1/lessons1.shtml) which is a little long in the tooth but little changes with languages over such a relatively short time and has both more of a grammatical focus as well as supporting documentation you can also download. There is also a good initial grammar guide available from the BBC (http://www.bbc.co.uk/wales/learnwelsh/pdf/welshgrammar_allrules.pdf). I have several other welsh course books I could direct you towards if these links are not suitable, but I haven't delved into these much as I have had enough to cope with attending classes in person. I do dip into another book: Teach Yourself Welsh Grammar by Christine Jones (http://www.amazon.co.uk/exec/obidos/ASIN/0340887869/) - this has useful exercises to reinforce learning as well.
Re: 2 -
To be honest I use electronic dictionaries 99% of the time - at least until recently when my wife lost our Android Tablet (!) as Ap Geriaiduron (http://www.bangor.ac.uk/canolfanbedwyr/ap_geiriaduron.php.en) is available for Apple and Android devices. Check out the rest of the Canolfan Bedwyr site as well as they run several projects of interest. The BBC site (http://www.bbc.co.uk/wales/welshdictionary/en-cy/ runs off the same database I understand. Also for vocab Google Translate (https://translate.google.com/) isn't too bad at all, just don't tax it too much with grammar. As far as hardcopy dictionaries are concerned 'Y Geiriadur Mawr' by Christopher Davies, published by Gomer is the standard recommendation once you're past beginners dictionaries.
Re: 3 -
I am going to point you at 'Y Lolfa' and, particularly, their 'Stori Sydyn' series. I will also recommend the works of Bethan Gwanas and, particularly, her Blodwen Jones trilogy which are part of the 'Nofelau Nawr' series for learners. Unlike some books aimed at learners these entertain as well as introduce you to new parts of the language. I would say that any of these probably aren't any more complex than Harry Potter, but they are more Welsh!