I suggest you to go with Electrum, it's one of the best wallets for storing your Bitcoin. If you really want to have 100% security then I suggest you to buy a separate laptop and install an operating system in it and after installing a fresh copy of the operating system, then you should install electrum wallet or just use it's portable version.

Create your wallet on Electrum and save your seed phrase on a safe location. I suggest you to save one copy of your seed phrase on your device's hard drive or ssd and another copy of it on a paper. Make sure to backup multiple copies of it in order to be safe from losing it. Then create your wallet address at Electrum and deposit your Bitcoin into that wallet.

After that disconnect that laptop from internet. That way you have an air-gapped system and your Bitcoin are 100% safe. I suggest you to copy your wallet address and whenever you need to deposit more Bitcoin use that wallet address only not that laptop.