I'm wondering about bootable backup strategies

Question

I'm wondering what people use and recommend for backup strategies, and especially the utility of "bootable" backups.
I have an early-2011 15" MBPro, running fully updated Yosemite.  My computer is apparently one of the "victims" of the recently publicized graphics system problems that has resulted in Apple's recent out-of-warranty repair offer for machines in this category.  Over the past 10 months my machine has been in for repair 4 times, resulting in the replacement of my display, main logic board (x 3!!) and hard drive.  These 4 repairs were the result of incidents that started with the screen graphics going crazy and ending, eventually, in an un-bootable state.  Two of the 4 times I was returned a working machine with a clean new-install of OS 10.  (all "free" I might add, thanks to still being on Apple Care when the whole process started!)  Hopefully, my last repair will "do the trick" as it was AFTER Apple's announced repair offer for these machines.  My Apple Store "genius" opined that this time my main logic board was probably an "improved" item, since the first two replacements didn't solve the problem.
So twice in the recent past I have had to completely restore my machine from my Time Machine (to Time Capsule) back-up.  Both successful, thankfully!  But this experience has focused my attention very sharply on my backup strategy, and made me wonder how "exposed" one still might be with "just" a Time Machine backup.
Talking informally with several more knowledgeable and experienced "Mac" people that I know, I discovered that many people don't rely on Time Machine, at least not solely.  I was persuaded that the really most secure situation is to have a second back-up, preferably a bootable "disc image,"  stored on a separate device (and maybe preferably off site).
So, I've been looking into the options, services, etc..  There are MANY!  I love the ease, automaticity and utility of having a Time Machine back-up.  But I'm wondering, for those (probably few) out there that do something MORE than that: what back-up strategies do you use?  Is is POSSIBLE to have a "bootable" backup on an online/cloud device (maybe not)?  What systems work well and are complementary/supplementary to Time Machine? 
I know, from my own experience, that HAVING a backup is fairly easy.  But I've also learned that RESTORING a backup (mine's around 400 GB) is NOT "easy", at least very time consuming, and probably fraught with potential problems which won't appear until it's too late to do something else!  So I'm particularly looking at the restoration features of backup software and services.  Frankly, those are often largely ignored in the promotions, which mainly focus on how easy it is to DO the backup but never talk much about doing the restore!!
Any and all opinions are welcomed.  I am definitely considering some redundancy in my backups after "dodging the bullet" twice in the last 3 months!

Answer 1

... how "exposed" one still might be with "just" a Time Machine backup.
Just one backup isn't enough. Two or more are preferable. Time Machine can back up to as many external devices as you wish. Purchase two or more inexpensive USB hard disk drives and store one of them offsite at all times. Time Machine will back up to each one "in rotation" when they're available. If the backup device it's expecting isn't available, it looks for the next one, etc.
If you want to augment Time Machine with another backup strategy, consider "clone" software such as Carbon Copy Cloner. It will create bootable copies of your existing installation if you consider that a valuable option.
"Bootable" is fine but not really necessary. Consider the possibility in which it's impossible to boot your Mac for whatever reason, or if should happen to be lost, stolen, or irreparably damaged. Consider the circumstances applicable to the way you use your Macs that might cause that event. If your disaster recovery plan addresses that contingency, it's a good plan. Recovering 400 GB is going to be time consuming no matter what method you use. An external HDD with a Thunderbolt interface would be fastest, followed by USB3, followed by USB2, followed by a directly connected (Ethernet cable) Time Capsule, followed by a wireless Time Capsule — for which a TM restoration might take an unacceptable amount of time (days).
Obviously I don't know the circumstances of the repairs you required, but I question the necessity to replace the hard disk. It's possible the same one could have been re-used, saving you the inconvenience of having to perform a restoration.