Well I made the experience from my countless beds around the world that the items on the floor stay there.

What I did not take into account that in these cases, the items were always in the radius of the workbench!

And when I built the house, I had to move the workbench: destroy it and rebuild it.

So there might have been times when there was no workbench.

However, I was able to restore all my items (took the numbers from an older savegame) using the following commands:

spawn Amber 17 1
spawn Amber 20 1
spawn AncientSeed 1 1
spawn AncientSeed 3 1
spawn AncientSeed 10 1
spawn BeechSeeds 73 1
spawn RawMeat 3 1
spawn TrophyBoar 7 1
spawn TrophyBoar 11 1
spawn Bonefragments 50 1
spawn Bonefragments 1 1
spawn Bonefragments 15 1
spawn BukePerries 1 1
spawn Bukeperries 1 1
spawn CarrotSeeds 6 1
spawn CarrotSeeds 13 1
spawn Coal 44 1
spawn Coal 5 1
spawn Coins 562 1
spawn Coins 20 1
spawn CopperOre 21 1
spawn Dandelion 9 1
spawn DeerHide 37 1
spawn TrophyDeer 10 1
spawn TrophyDeer 6 1
spawn Feathers 50 1
spawn Feathers 31 1
spawn FirCone 7 1
spawn Flint 7 1
spawn FlintSpear 1 1
spawn TrophyGreydwarfBrute 1 1
spawn GreydwarfEye 50 1
spawn GreydwarfEye 4 1
spawn GreydwarfEye 25 1
spawn GreydwarfEye 19 1
spawn TrophyGreydwarf 20 1
spawn Hammer 1 1
spawn Hammer 1 1
spawn HardAntler 2 1
spawn ArmorLeatherLegs 1 1
spawn LeatherScraps 30 1
spawn PineCone 7 1
spawn ArmorRagsLegs 1 1
spawn ArmorRagsChest 1 1
spawn ArmorRagsChest 1 1
spawn ArmorRagsChest 1 1
spawn Resin 50 1
spawn Resin 5 1
spawn Resin 50 1
spawn Resin 50 1
spawn Resin 47 1
spawn Ruby 20 1
spawn Ruby 4 1
spawn TrophySkeleton 1 1
spawn TrophySkeleton 2 1
spawn TrophySkeleton 5 1
spawn AxeStone 1 1
spawn SurtlingCore 7 1
spawn Thistle 18 1
spawn TinOre 16 1
spawn TrollHide 40 1
spawn TrollHIde 20 1
spawn TrollHIde 3 1
spawn TrophyForestTroll 2 1
spawn TrophyForestTroll 4 1

Just in case anyone else has this problem.

Valheim has to be started with the -console option. The console can be opened using F5.

Thanks for your tipps guys!