There is no apology needed, except from me to you. No, you didn't hit a nerve,.......sometimes my answers get a little too emphatic for my own good. The point I was trying to get across is this: the welt foot is absolutely essential if you are sewing welts.
I didn't notice that you were in Australia when I answered your questions. I'm sure locating and buying the correct supplies and equipment is a heck of a challenge for you.
Please take this advice, which I tell everyone who buys a used machine: Throw away the thread that came with the machine and start over with brand new thread (and bobbins if pre-wound ones came with your machine). It could be as simple as bad thread. Why risk doing work that could come apart prematurely and getting a bad reputation when it can be so easily avoided? Good Luck, and G'day to you, too.
No one lives forever, the trick is creating something that will.