I have always supported the method of keep buying the more money you have every x time period instead of going all in all at once.
If you spend $10k all at once then you may end up losing money (you can profit as well) but if you just spend $1k each month for 10 months you can have a decent average, doesn't matter if it goes up or down, you will be closer to whatever the price is right now compared to person who got all in. That is why I keep making bitcoins all the time and spending some of it and saving some of it every single month, I had times where I cashed out at $20k, I had times where I cashed out at $3k, I had times I got paid at $20k, I got times I got paid in $3k.
Hence, it makes like a decent average where you are never too far away from the most recent price.
I am a big advocate of monthly SIPs but it is important to remember, even if you invest in a SIP format, your investment won't be safe in the crypto market for long. Especially due to the heavy swings that comes with this space. So there is no alternative, at least in my mind, other than being an active investor, moving your funds around from one asset to another. A successful trader manages his money, or hires someone to manage his money in exactly the same fashion.
And this is not only limited to traders, many wealthy European and middle eastern households frequently employ these money management consultancy firms to handle and safeguard huge fortune that might have been accumulated over centuries.