Form-fitting Bodysuit Tutorial
First off, you will need a duct tape dummy for this. I suppose it is possible to do this without one but you will need a close friend/family member who is willing to spend several hours with you, while you are practically naked, and touch you pretty much everywhere. I'll go on the assumption that you have a dummy of some sort, since doing this on your own will not be easy.
A JUMPSUIT PATTERN
First step, go buy a pattern. Any will do as long as it is a jumpsuit of some kind (top and bottoms attached). I used a pattern for pajamas, you can also get patterns for actual halloween costumes. Second step is to find the closest approximation to your size, and then sew it up using cheap material such as old bedsheets. Try to use something that does not stretch or your results will not be accurate. I am going to assume you know enough about sewing to do this without guidence, if not, there are other places you can learn how to sew. Jumpsuits are pretty easy though, mostly straight lines and no tricky bits, and we don't care about things like zippers and interfacing at this point and you're just going to cut this apart later.
BASIC BODYSUIT PATTERN PIECES
Step three, put your bodysuit on your dummy (or vise versa) and begin pinning it in. Or a stapler works too. Try to resist creating new seams and just pin in the ones already there. Make sure you don't make it so tight that you can't move. I prefer to keep places like under the arms and the crotch fairly loose. After all, this bodysuit is supposed to be comfortable. You can add darts if necessary and you will probably have to if you have breasts and want a tight fit.Now, take it off the dummy, sew it up and remove all the pins. Try it on to make sure it fits well and to do any last adjustments. Now take it apart.
MARKED UP BODYSUIT
I just cut the material right next to the seam. This will leave no seam allowance, but you can add that later. You really only need to keep half of the suit ( especially as you want both sides to match). So pick a right or left and keep the front, back, and arm from that side.Lay them flat and trace them onto stiff paper. If you don't have any and you want to keep these patterns for future suits, then trace them onto newspaper and layer the back with duct tape to stiffen it (and waterproof it too.. will the uses of duct tape never cease..) You can add your seam allowance here, if you want. I prefer to go without and to add it when actually cutting the material. You can also even out your pattern here, making sure all the things that have to match up do. Like the lengths of the back and front leg seam, and the back and front arm seam matching the arm. Basically, everwhere two pieces of material meet. Now that you have a pattern, I want you to go find more scrap material to cut out and sew up into another bodysuit. This may seem like a repition of the first couple steps, but this time you're sewing up your own pattern, and you want to make darn sure it fits before cutting up the expensive stuff. As well, what you just made was a pattern for a basic form-fitting bodysuit. This is where you tailor that pattern towards whatever particular suit you're making. Now, run and sew up another scrap bodysuit using *your* pattern this time.
FINISHED BODYSUIT, READY FOR FINAL ADJUSTMENTS
All sewn up? Good. Does it fit? If so, very good! Otherwise, make your alterations and then make them to the patterns you used as well. Now, this is the fun part, take the suit off and put it on your dummy. Then take out a marker and draw on your character's markings. Use a lighter coloured felt first and then, when you're totally satisfied, go over it in thick black marker. Don't forget to label your pieces before you cut them out. If possible, it is best to use straight lines and use the existing seams as much as you can. And don't mess with the crotch and under arms- many seams come together there and it'll just get difficult. Cut the new bodysuit up on the seam lines you drew and the original ones. It may be possible here to minimize the number of seams by not cutting apart some original seams (example, if you have a belly panel, you may not need to use the original seam going down the middle of the belly). Just keep in mind that the more seams there are, the more body-hugging this suit will be and removing seams can make things slightly more complicated to put together and it needs to be measured exactly to prevent lumps (such as at 'T' seam intersections). Unless you plan to use this same pattern in the future, you don't even need to transfer the fabric patterns to paper, just trace straight onto the appropriate fur.
Cut out the fur pieces and sew them together (you should be getting pretty good at sewing by now with all this practice). Of course, you need a zipper or other fastener(s) but the instructions that came with your jumpsuit pattern still apply, and just refer back to that if you have troubles.As well, if you are like me, you add more seam allowance than you actually sew, so the suit may fit a bit loose. That is good, gradually take in seams (put the suit on the dummy inside out and mark all the loose seams) until it fits how you want. I prefer to error on the side of caution and piecing material in between seams (to make the suit bigger) is not fun.Then, a last step before adding a tail etc, if you have not already, trim all your seams and then go over them with a zig-zag stitch. Or serge them. You want strong, skinny seams. And there you go, the comfortable, form-fitting bodysuit I promised. Add paws, a tail, and a head and you have a full costume.