If you "double" the income of people living at or below the poverty line, you do not double their buying power. Mile that cost $2/L will now cost $4/L, rent will skyrocket, because more "welfare" will be available.
I wholly support the concept of UBI. But it can ONLY work if we restrict how much corporations can charge. Some things that would help in that regard: restrict the $ divide between the highest paid and lowest paid positions in a corporation.