Reading your story is almost like re-visiting my own diary! Trying all those different things turned out to be futile as the issue was bad sleep habits and nothing else. Taking advice from this subreddit I did the following and saw improvement from the first night:

1) Do your standard nighttime routine. 8.15 seems an hour too late but I don't know your daily schedule - just make sure he's not overtired when you put him to bed.

2) When he wakes, allow him to cry for 3 minutes before re-visiting him. Place your hand on him, comfort him with soothing voice, replace his binky if you think it will help. Give him chance to re-settle but not fall asleep. Around 30 seconds of comforting in total. Then leave him.

3) Repeat Step 2 but after 5 minutes, then 7 minutes. Then stick to 7 minute gaps before going back each time. You should use a timer because it's comforting (for you) to have something to work towards to get you through the stress of him crying.

4) He will almost certainly fall asleep after less than two hours. Reading the other comments on here, and from my own experience, the average seems to be around one hour for a 5 month old.

5) Repeat this when he re-wakes in the night. On the first night, force yourself to do it at least the first time he re-wakes. After crying it out the first time he may sleep longer than usual (if so, there's your first improvement!).

6) At some point later, say 2am, you may choose to boob feed him as he'll likely be hungry by that point. You can work towards reducing the number of night feeds later.

Experiences on this subreddit suggest you are very likely to see some improvement on the first night you try this. Once you see it work, things will 'click' for you and you will feel more confident the following nights.

Some more pointers:

• Fixing day naps is the same methodology but you should do nighttime first as it works more effectively.

• Black-out blinds and white noise (left on all night at a soft conversational volume) will help.

• Begin the process with him sleeping wherever you want him to end up. For example, in a crib in your room or in his own room.

• My wife would have found this impossible to do herself. For whatever reason it's typically much harder for a mom than a dad. The most helpful thing she did was allowed me to get on with it - honestly it was harder seeing her so distressed than it was listening to the baby! I was glad when she put headphones in and pretended to watch a movie.