いいです。

It's perfectly correct. ～するつもりです usually means you have the concrete plan or the will to do something, and I see no discrepancies in meaning. Alternatively You could write "私は日本へ旅行に行きます。"　to state your plan simply. Or maybe you could also say "私は日本へ旅行に行く予定です。"　but these are just variations.