"I'll travel next week" = your decision to choose next weak over other options. If you have just reached a decision when to travel, you express your decision by saying "I'll......". "I'll be traveling next week." = tells people what you will be doing next week. It is not a decision. A bit tricky, but yeah, English isn't easy.

I'll travel next week'' is simple future...... ''I'll be traveling next week: is future continuous ... so there is no difference on grammar

- We use the future simple to express a spontaneous intention: 'I'll travel next week'. - We use the future continuous to talk about a temporary action that will be in progress at a time in the future: 'I'll be travelling next week'. Compare: - We'll have dinner at 8.00, shall we?= It is a spontaneous intention. Here, functionally, it is a suggestion. (Dinner starts at 8.00) - Don't call at 8.00. We'll be having dinner. = It is a temporary action that will be in progress at a time in the future. (Dinner starts before 8.00)