There is advice aplenty here and even how-to videos -- people are trying to help you, and you're arguing the toss with every bit of advice given to you, and then you're surprised when they become exasperated. To be honest, if I were you I'd take the bass to a luthier, pay him for his expertise and ask him very nicely if he'll be kind enough to talk you through how he does it. He might, he might not, but either way it'll be £30/whatever well spent. Don't argue with him though.
Oh, and if you're going to press ahead and DIY, you'll never get anywhere with your 70p Wilko POS. Go onto ebay and search for "engineer's rule". You can pick them up for a couple of quid.