First off I totally agree with Jemma about the pull ups, when I worked with toddlers and it was potty training time I really did my best to talk parents into not using them if possible. One other thing to try is if you have 2 bathrooms let him make a choice as to which one he wants to use, if not maybe try getting a potty chair as an alternative. Another thing is to let him pick out a picture or 2 to hang in the bathroom or a special game only to be used at potty time. Good Luck ☺
Just put on normal underpants.
When it is warm, let him run around with no pants on.
There will be some mishaps. Keep a potty near him all the time.
If he is short, get a small stool so that he can stand on it so that he can pee into the toilet pan, whilst he is standing up. You can put some tissue paper in the pan and get him to aim for it.
Don't give in to him and persevere with the potty training.
If you keep putting on the pull ups, psychologically he is getting the message that there is no point going to sit on a potty.
When he wets himself a few times and it is very uncomfortable, he will learn much quicker.
You can still put on pull ups at night time as children can be much slower with regard to not wetting the bed at night or getting up when they need to pee when they are asleep.