Twll! I would gladly send you some of the heat, I'm getting fed up with it!
I hope ymarferiadau means "exercises". I mean "physical exercises", based around swimming.
I would have said in your sentence: Dw i'm meddwl bod y cysondeb yn bwysig iawn
I don't get the "fod bod" thing either.
If I got stuck I might rephrase mae'n rhaid i ni fod yn gyson, mae peth yn bwysig iawn
If you do find yourself getting tied up in a phrase, just relax, don't worry too much about it, and if you can rephrase, then do it as naturally as possible - we have all lost our thread in a sentence in English at one time or another, or if you can't rephrase, then let it go. Don't freeze and turn it into a major problem.
When I had my first job interview in Greek, no option at all to fall back on English, I found the best thing to do was relax, and not be afraid to admit your limits. If they use a word you don't know, don't agonise over it. Ask them to repeat/ rephrase and remember they don't expect you to be like a native speaker, you are not applying for a translation position!
Best of luck! Pob lwc!