Just buy them on any CEX you find easy to use and let it be there. Kraken is the most trusted and followed by Coinbase.
Instead of being a nerd, creating your own wallets and risking it to various malicious attacks, I would just simply trust the companies who are spending millions on security.
I don't know why another member didn't compare this post if saving and keeping the crypto on exchange is not safe and dangerous. We already know, the exchange is a third party where we don't own the private key, which means we don't own our treasure. Exchange, even if the company who have spent millions of dollar money, but we don't know next, we are of corse aware and understand what happened in other exchanges like MTgox, FTX and the latest one is
Hotbit.
I definitely wouldn't dare to save in exchange for 1 satoshi even if that exchange has spent multi-trillion dollars.
Remember that disasters especially in cases of fire, flood, war and even earth quakes can't be easily predicted and at such I think your method is obsolete and I don't even feel safe using a hardware wallet despite its cost
That even better to lose it by myself in a safebox than lost stolen by Google, Apple, or other clouds.
For someone who is only making use of a mobile device for now, will it be safe to still download and use Electrum wallet on the mobile, seeing that there is no other device except on an OTG flash where I can save this wallet?
You have to root your phone to know the wallet file, but I won't be recommended it if you are not familiar with that.
I think saving bitcoin in a hardware device is one of the safest ways to save bitcoin for the future,because you don't need to panic if the hardware breaks, get burnt or stolen, all you need is just to secure your passphrase and you're good to go.
It depends on you, I have a friend who has a hardware wallet stolen in his drawer. My method above is free, you don't need to spend the money to buy a hardware wallet.