Amateur Rider Needing Help with Buying a New Bike

Don't want to read the back story, skip to second paragraph

A couple years ago I did my first ever bike race and rode a friend's bike. It was the first nice bike I'd ridden and wanted one of my own afterwards. Found a 2006(ish) Bianchi Axis in near perfect condition at a garage sale with a mechanic stand, extra set of tires, and Cateye setup for $400. Snatched that up only to later find out that bikes have sizes. Turns out mine is about 2-3 cm too small for me. I moved the seat back as far as it will go and have the seat post extended as high as the safety line will allow. I take it out 30-40 miles a week but it's a little uncomfortable and I know I'm not getting the most out of my rides since I'm bunched up and can't fully extend my legs. I'm to the point where I can average about 15mph for a two hour ride on long days and 16 mph (hills depending) on shorter rides.

I need a new bike but have no idea where to start. All I know is I want the right size, disk brakes, and a similar gearing setup. Currently have a Shimano 9x3. I'd like to get a carbon fiber frame like the one I have now, but I'm not sure I could afford it on a new bike. I'm 6'1" and a fairly lean 230 lbs. Rather big rider, but loving it nonetheless. Thanks for reading.