British Expats - Widow of British citizen with British son

I am a filipino, a widow to a british citizen and has a british citizen son. My son wanted to go the UK so I have applied for family permit from the Philippine British Embassy so I could take my son for a visit and possibly settle in UK if he likes it. ECO emailed me after a week or so to tell me to withraw my previous family permit application and apply for a visit visa and pay the necessary fees. I did that. Now, I got my visitor's visa approved. What if my son decides to stay and take his education in the UK? Can I also stay and be able to switch to another kind of visa or apply for a family permitagain? My visa expires 5 months. Should I let my visit visa expire and apply to settle as primary carer? Or can I apply anytime even with a valid visitor's visa? Would it really matter? Whats the best visa for me? I was on settlement spouse visa before in the UK with my husband until it expired and I came home as I was not aware that I could apply for ILR then. Its been 9 years since a last left the UK. I studied a degree in college in the PH after coming home without reapplying any form of visa until now. I need your help. What should I do?