Generally, strapless tops only look good on rail thin, narrow shouldered, petite women. Skip them this year. From what I've seen by designers, they're not really in vogue this year anyway.
And there are many bras out there to give you the appearance of cleavage. Sometimes though it helps to have athletuc tape, two bras, or little padded forms to help push you out there. ;-) just try various techniques, every girl's needs are different.
Are you one a low dosage of estradiol? And maybe your testosterone levels are still to high and thereby still contradicting any possible benefit of estrogen...