It's true that you should dress the body you're in, unless you actively involved in a weight changing regimen.
So what do you do?
First, save up at least 80% of your shopping money to invest in a new wardrobe once you've hit your goal. This way you can reward yourself, and your fans, by stepping out in a new body adorned with new clothes.
Second, do an inventory of your current most comfortable pieces. The pieces that you wear to work, out with friends, and to casual activities. What are those pieces? Instead of looking at an item as your favorite designer dress, look at it as a light weight cotton blend dress. Make note of all the details that make it your favorite piece. Then shop for those specific items discounted as your weight changes. The important part of this is you remain nicely dressed and comfortable as your body changes, but you aren't breaking the bank on clothing you won't be in for too long. I spend extra time in Old Navy and Target during this time. You can find beautiful pieces for super cheap!
Third, go accessories insane! The only thing that won't change sizes are accessories.
I have invested in belts of every type and color, because they are adjustable and can create a waist even on an item a little too large. Belt a top outside of your pants, blouse your top just a smidge, and look how tiny you waist instantly is.
Invest in scarves, because they can be paired with anything during the spring and fall and pull attention up towards your face. You can tie some scouts knot or just wear them hanging long and open. It's a great way to jazz up a cheap tee or tank too.
I BELIEVE in jewelry for the same reason. Jewelry demands attention. You can dress in denim and a white t-shirt, but with jewels you will immediately look more pulled together and expensive. Jewels will draw the eye where ever they are. It's a well known fact! Ask anyone.
Fourth, and my fav, get creative.
I have a friend who added 1000, elaborating, colorful safety pins to the neck line of a v-neck tee from Target. Wowza! It is adorable and cost her less than $5. Plus when her size changes again, and she has lots of time on her hands, she can just switch the pins to another tee. I don't recommend you go crafty on your entire wardrobe if it's not in your blood though. Just look for different ways to cut cost and sizes with your changing body.
Buy every color of slinky t-shirt at your favorite store. As long as it doesn't have a pocket you can pull it off even in the office. Just go back to step 3.
Purchase dresses. Dresses can last longer than pants with body changes. They don't show change as quickly and obviously as pants tend to.
In general, be creative.
Play up your favorite features, and play down your imperfections.