I gave a flip and funny asnwer to this last time, so I will give you what one of my followers - Jessie Pinkalicious said .. here goes!
You might first look online at ANY women's clothing retailer and check the SIZING CHART! Get a fabric measuring tape (any drug store / chemists) and FIND YOUR CORRECT WOMEN'S SIZE!
Now I would suggest first trying a thrift store or used clothing store. The Salvation Army (in the US) is a great source of really cheap and decent clothes! You can alway say you're shopping for your sick mother! :-)
When you learn what sizes you really are (the clothes will vary) now you can try it for real! Go to any store you like - you might feel more comfortable going a little bit away from your local area the first few times to avoid seeing folks you might know... but be BOLD! Go in and look around... see what you might like... look for your correct size... and when you have a sales lady ask if she can assist you... SAY YES!
Now... you might just decide to bite the bullet and tell her the truth! Believe me when I tell you they have heard it ALL before! OR if you aren't yet ready for that step... tell her you are dressing as a woman for a costume (fancy dress) party and need to REALLY look good!
She will see right through your ploy, but who cares! And from then on... try everything on and see if it fits! Get a whole outfit! Top, Skirt, sweater, coat, scarf, hat, gloves, purse AND if they have it all... panties, bra, garter belt (suspender belt), stockings, and of course, SHOES!
Get one complete 100% head to tow GIRLY OUTFIT and thank her completely!
As for your makeup... I suggest MAC Cosmetics. They have a GENDER NEUTRAL POLICY! Meaning that they are TRAINED to provide makeup for both men and women... even if the men are trying to look like ladies! Just tell them the truth and they will do the rest!
If you are brave enough, ask for an in-store application... you will pretty much be required to at least buy SOME of what she uses on you... but you will LOVE THE LOOK! They also offer PRIVATE MAKEUP LESSONS - JUST ASK!
But most of all... ENJOY YOURSELF! You only live once... and nobody wants to be lying in their death bed at 90 wishing they had had the nerve to wear a pretty panties and bra set 40, 50, 60, 70 years ago!