Past perfect here

I am not sure whether the past perfect (1) is mandatory in cases like the following. I wonder if in everyday speech the versions with the simple past (2) would be just fine.

1)Damn, it doesn't work! I thought I'd found a solution, but this is totally useless!
2)Damn, it doesn't work! I thought I found a solution, but this is totally useless!

1)I thought your mother had died, that's why I was trying to avoid talking about her.
2)I thought your mother died, that's why I was trying to avoid talking about her.

1)I knew Jack had given her that money, so I was trying to find it. I felt she'd probably hidden it in the kitchen.
1)I knew Jack gave her that money, so I was trying to find it. I felt she probably hid it in the kitchen.

Thanks.

In the first pair I think both versions are perfectly acceptable, although if you were writing you'd probably want to choose the past perfect.

In the last pair the two sentences indicate different things.
"I knew Jack had given her that money" shows that this was a single incident at a particular past time.
"I knew Jack gave her that money" tends to imply that the giving of money is not isolated to a single event but could be an action that repeats itself even now.
The same difference could apply to the second pair of senteces, although the sense of the sentence excludes any lilkely confusion. Past perfect is definitely more appropriate but the past simple would get by okay.

I see, thanks.