If I start playing it after a few months of not playing it, my thumbs get sore too. After a few hours I stop playing it and maybe the next day or so when I play again, it hurts less. You might just be needing some rest for your poor thumbs. If you start feeling pain you should definitely give it a rest - don't keep playing until your thumbs literally fall off, right?
You might also want to consider trying out different controllers - there might be a model which has less resistance in the thumbsticks, which would make things easier to move.
In terms of strategy, I noticed that I do try to go for the same patches of clustered objects that are just barely grab-able - this helps me grow the katamari the fastest. Things like sunflowers, desks, and especially trees tend to clump together - once you can get one, you get like 20 in the same area. Same with boats, buildings and the open-sea fishing pens (although if you can get to that size you probably have the hang of it). Fences also seem to help it grow fast but they can get annoying with their odd shapes.
Also, look for things that are actually a collection of inter-touching objects, like a stack of lego-type blocks, or the red mailboxes in the town, or a wall of bricks where each brick is a separate object - you can gain size pretty quickly with those also.
Katamari Damacy is the English adaptation of the Japanese romaji Katamari Damashī (kanji: 塊魂, hiragana: かたまり だましい), which means lump/chunk soul.
Best Answer
No there ist no demo of Katamari Damacy available for the PC, only for the Nintendo Switch. To test the game on PC, you could buy it on Steam and return it within the refund time period, if you don't like it.