Next week I will go on holiday to a foreign country and for this I bought a prepaid SIM card because with my phone's current plan I have little to none data in Roaming. My problem is that I will be using my phone with this new card, but I would still like to use my current Whatsapp account. The only solution I have come up with is changing my number in my Whatsapp account's settings, but I wouldn't really want to do that because it notifies all my active conversations. So, is there anything else I can do so that I should be able to still use my Whatsapp with this prepaid SIM card?
Yes, you are actually in the right direction. WhatsApp requires a SIM for installation and activation. But once activated, it doesn't matter if the SIM stays in the same phone or is tossed to a different phone, or even lost. Sure, in cases of lost SIM, re-installing WhatsApp with the same phone number will be impossible.
WhatsApp will keep on working on your phone, provided you have a data connection (no matter which SIM it comes from) or WiFi access.
So, yep, just toss in your prepaid SIM, turn on data connection and continue to use your old (current) WhatsApp. You do not have to make any changes in WhatsApp. Changing the number is also absolutely NOT NEEDED. It is only used when you are officially switching to a different number and would like to carry your chats along.