Perhaps: 'I'm very/most/extremely grateful (+ to + person) (+ for + object) eg I'm extremely grateful for all your help I'm very grateful to everyone who helped. Or use the verb 'appreciate' eg I really appreciate all the help you've given me on this project The phrase 'Much obliged' exists, but it can sound a bit dismissive. NB avoid using the word 'thankful'. It isn't a synonym of 'grateful', as it has a slightly different meaning.

Even more naturally, you could say, "Thanks, I (really) appreciate it." or "Thank you very much."