Because we were able to talk thoroughly regarding the contract, we each felt comfortable about signing the contract.
"Because we were able to talk thoroughly"=「私達は細かい点まで徹底的に話し合えたから」
"regarding the contract"=「契約に関して」
"we each felt comfortable"=「私達はお互い心配なかった」
(☆「納得して」を"comfortable"と訳しました)
"about signing the contract"=「契約を結ぶことについて」
ご参考になれば幸いです!