Buy on strike and withdraw over lightning to Phoenix wallet. Phoenix is one of the easiest to use self custody wallets, and it gives you a seed phrase. Since strike is custodial, they will handle opening the channel when you withdraw to Phoenix so you don't pay a big channel opening fee yourself. IMO that's the best solution right now.
You can download strike, set it up, link a debit card, deposit, buy Bitcoin, withdraw and have it available in your Phoenix wallet all in under five minutes.