Hey guys. Need some info on travelling to England.

Where can I get info on preparing a letter of support? And what proof is needed with it? (this is for my boyfriend in england)

My daughter and I are travelling to go visit him for about 3 1/2 months and I know we will need proof of funds. I figured about $1000 a month would suffice because that's only a little less than we survive on now. And with the letter of support, we should have no issues.

What do you guys think?