Congratulations! You give me hope. We've been trying for a while ourselves.
Before asking for extraneous ultrasounds, please, please, please read the information on the risks of ultrasounds. You can find some great information on that here
As for baby blankets, I don't know there's really any "risk" with them... I still have my baby blankets from when I was little, and they ran the gamut from quilted to crocheted with lots of large holes. I have every intention of using them with my children when the time comes.
There are great patterns at knittinpatterncentral, or you can just do a seed stitch, garter stitch ,stockinette stitch, basketweave, whatever you like with or without a border, in a solid or stripes. Blankets don't require a pattern unless you want to get intricate. Best of luck!