I hope your new found motivator works for you, and wish you all the best on your journey. It is my strong opinion that sex is not a gift a partner doles out as a reward. My wife has joked, testing those waters a few times, and I’ve let her know my feeling, that sex is the physical manifestation of the love we share for each other. It is not a currency.
This is so wrong. I wouldn’t pursue this path. Intimacy needs to be shared and mutual. Is she in shape and you’re not? Could she stand to lose a bit too? Just trying to get a feel for the dynamic and variables between the two of you. Is there currently mutual attraction?