you been married along time, have a son - so the embassy cannot say your relationship is not genuine
where are you living now, i take it, it will not be over crowded when you wife and son come ?
cab i think are right, so do as they say, you're working which is most important, you also have savings, as long as you have about £100 a week left after paying rent/util bills you should be ok..
as for 3 months being self employed, if you have an accountant ask them to help you do your projected forecast..
good luck, thou i think you shouldn't have a problem getting your visa
