First of all. Mass gainer is already full of sugar and artificial flavoring. No way you can get something lower than whey protein. Even if you take mass gainer and reach certain weight but will you able to maintain it? Impossible you want to take mass gainer for life.

The best way is to start changing your diet. Add more food or meals throughout the day. Can add snacks as well. This way you can gain weight and maintain it for life. Maybe you can start adding oats to aid your cholesterol issue as well.

Most ppl manage to get few extra KGs when they first workout. Those are water weight. Your muscle tend to store more glycogen so you will be able to use it more.

You're skinny because your calorie intake (eat/drink) is less than your calorie out (exercise/moving around). Not because of the protein that you take.

I see you're from Klang. I can help you understand more about workout & nutrition if you can meet me at Bayu (i always workout there). Ghetto gym if u dun mind.