There are a lot of issues going on here. There are regional differences for a start - Jawon has given you an American perspective, which is based on an English usage which different from the English you have learnt. For him, ''Thank you very much' is 'weird', while for anyone who speaks British English like you do, this is the most normal and standard way of expressing polite gratitude. There's also possibly an age and even a gender issue. I think that 'Thank you ever so much' sounds fine, and it's something which I often say myself, but I wouldn't imagine a young man saying this, somehow. As for 'indeed', you can't add 'indeed' on the end of 'Thank you ever so much', because it's already intensified with the 'ever so'. But you can certainly say 'Thank you very much indeed.' I think that Paul definitely has a point about overly polite expressions of thanks sounding sarcastic, and as native speakers we are very attuned to subtleties of intonation which might suggest insincerity. I don't think that this is an issue for you as a non-native speaker, though. So, if you want my advice, carry on saying 'Thank you ever so much' or vary it with 'Thank you very much indeed'. They sound fine, and nobody will misunderstand your intention.

Those words are polite but I don't know, maybe they are a bit too polite. Maybe it's just me and my cynical nature but I can't read those words without thinking of someone saying them in a sarcastic tone of voice. You ask about the nuance of 'indeed' and to me it has the connotation of being a bit patronising and overly servile. It's perhaps a bit different if a non-native speaker says it but if a native speaker said these phrases I think they run the risk of people thinking they're being insincere. 'Thanks a lot for your help/thanks for your help (I really appreciate it') would be what I would say.

I think that the better way to say that is "Thank you so much"(more formal) or "Thanks a lot"(more informal). I've actually never heard someone say "thank you very much". It kind of sounds weird to me... Also, I've never heard someone use "indeed" in that phrase.