What country are you from? There might be a Bitcoin ETF or equivalent and you can buy that with your stock trading platform.

You can use an exchange such as Binanace and just keep it on the exchange. Don't need a software or hardware wallet, its just for extra protection. If you keep it on an exchange just make sure you use 2FA and don't reuse passwords. As long as you don't click phishing links in email or anything suspicious you should be fine. Also enable whitelisting addresses also as an extra protection.