How is this word spelt in modern Irish ? - bhéidheas. Here's the context -

Am air bith a bhéideas lionn nó fíon ag teastáil uait.....

Here's something else -
Air maidin, lá air na mhárach, chuaidh Páidín a bhaile agus thug a bhean agus a chlann go dtí an teach mór, agus bhíodar go sona.

That last word I would have translated as - happy, but in fact, with - go - in front of it, it should really be the adverb - happily, but of course that doesn't work here.
Douglas Hyde has translated it as - they were comfortable. I'm not saying that that is wrong, but it does seem to me an interpretation on his part. But again he is back in 1890, so the two languages have evolved since then.
But here's another example going the other way - this is taken from the story called The Brown-hired boy, of which I only have the English version, where he goes off to seek his fortune, he gets it and comes back to his poor mother -

And as soon as he came home he gave fistfuls of gold to his mother, enough to keep the poor woman in comfort. Would - go sona - be appropriate here?

Compare:
Tá mé go hálainn.
Tá mé go maith.
Tá mé go dona.
Tá mé go sona.

The number of adjectives using "go" in sentences with the verb bí differs in dialects.
Sona often in the prase "Tá X go sona sásta" (X is happy and content.)

a bheidheas -> a bheas (a bheidh)

Go raibh maith agat

A bit further on, he says - táim - I thought that it was only in Munster that they said this, as I mentioned earlier he's from Mayo.

"Táim" is common in Connacht Irish (though "tá mé" is more common), rare only in Ulster.