Evidence of Support : It can be any combination of the following three :
_ Affidavit of Support : form I134 filled by a US Citizen ( USC ) or a Legal Permanent Resident ( LPR = GC holder )
http://www.uscis.gov/graphics/howdoi/affsupp.htm
_ Job offer in the US : it is better to obtain a job offer on the company's letterhead and have it notarized.
_ Own funds ( bank accounts, assets....): see poverty guidelines ( on
travel.state.gov ) for an idea of the amount. ( bank statement)
For the Evidence of Support, you can provide any combiantion of the 3, which means you can provide one ( any one ) of the mentioned documents, two ( any two ), or the three of them.
Remember that you better be safe than sorry. Bring as much as you can.
So, the I134 alone is good. Still, it would be better if you could show your own funds.
Also, education and english skills play a role as it will help in finding a job.
The immigration officer determines your potential to become public charge. So the more proofs you provide that you won't become one, the better for you.
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The above is my generic answer for questions on evidence of Support.
In your case, I would say you do not need a I134 as you already have a job in the US ( and you mention that your income is comfortable ) and have personal assets ( bank accounts, house...).
I would recommend to bring your tax returns and get a transcript from the IRS ( to prove that you did send the returns ) ( a transcript is free, an actual copy of your return is about 40$/year ).
You could also ask your employer ( HR ) to get you some kind of letter stating how long you have been with the company, how much you make...