Because there are so many parts to your question its tricky.
Getting more light into the heart of a bungalow is easy as you just put a rooflight into the pitched roof and a hole into your dining room ceiling- the cost depended on how big you go and how much you need to change the roof structure. This job varies between £2,500 for a single rooflight to £15k for a vaulted ceiling to the whole room with lots of glass.

Taking down a wall between a couple of rooms is easy especially in a bungalow where it’s not holding up another floor . Costs start at £2,000 but bare in mind you will no doubt need new flooring adding another £1200. Assuming you want doors to the garden rather than your current bedroom window I think you need an additional £3,500 but fancy Crittal doors could cost £10k. Then you might need a patio outside- size and materials dictate price- expect costs to start from £2,500
The front room as a bedroom seems straightforward - but you need to consider if you need to build in some wardrobes, in which case are there too many windows, or do the deeper windows of your current lounge create privacy issues for a bedroom- do you need shutters? And considering this is a large space do you want an Ensuite in which case the cost varies depending on where the drains are. Expect that to cost £10k -£16k.

Making this house work for you could ultimately be cheaper than moving and if it were mine I would also want a principal room to connect with the garden so you should go for it. Consider if a more radical change would be better because your plan appears to leave you with an undersized living room and still a conservatory that likely is underused because it’s off the second bedroom.

If you want additional creative ideas for layout then post a few measurements- specifically the lounge, kitchen, main bedroom and the room leading to the conservatory. Given the shape of the kitchen it seems like you might be on a corner plot so it would also be good to know where the garden is