Sorry Jamesie with what you're going through.
While you are peeing, can you stop mid stream? This is a very good way to find the right muscle to contract. It's possibly not a good way to exercise as it might cause retention if you repeatedly do it, but OK to try occasionally to make sure you have identified the right muscle, and to see how well it's working (by how quickly you can shut off the flow mid stream).
You appear to know some of the things that make you leak, so something to try is to do a pre-contraction before and while you stand up, and see if that prevents the leaking. Same with coughing, etc, and this will become instinctive.
Alcohol and caffeine are possible bladder irritants which if you are sensitive to them, will cause urgency (the sudden need to go before your bladder has filled up). That isn't the symptom you described, so it might not be necessary to give them up, but it does no harm to try these things out just to check.
You can ask for an appointment with a pelvic health physiotherapist. These specialise in muscle control relating to continence and can check you are doing your pelvic floor exercises correctly. They can also do more detailed measurement of the effectiveness of your sphincters if they think this is useful, e.g. if they suspect your sphincter isn't working correctly.
Also, if you're not getting the pads prescribed and find them expensive, ask your GP if you can have them on prescription. They will likely refer you to the local continence service, although this is a bit of a postcode lottery. Also, what you can get on prescription (if anything at all) might not be what you'd choose to use.